In the current war with Ukraine it seems like the West can send any forms of weapons (short of nuclear warheads) to Ukraine without causing the conflict to escalate beyond Ukraine’s borders. This includes long range weaponry capable of hitting military targets within Russia’s territory. However it seems like sending actual troops is out of the question as this would cause a significant escalation of the conflict.

Why is this the case? What’s the difference between sending a HIMARS launcher and sending a battalion of troops?

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  • Comments are not for extended discussion; this conversation has been moved to chat.
    – CDJB
    Sep 23, 2022 at 10:07
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    I don't have the expertise to formulate an answer, but I suspect it matters that, during the cold war, defence scholars from both sides published their thinking on what does and doesn't constitute an escalation, read each other's publications, and to some extent, reached a common understanding on the question. Sep 23, 2022 at 10:08
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    @DanielHatton care to add an answer listing said publications? Sep 23, 2022 at 15:04
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    Note that the West is NOT supplying all types of weapons. There are some categories that are sent, some not. There are very few weapons sent that would be useful for a counter-invasion into Russia, for example.
    – Tom
    Sep 24, 2022 at 16:24

15 Answers 15


Already many good answers, I just wanted to add another facet

The weapons change ownership; the soldiers don't.

If Poland (for example) sends a gun, a tank, an airplane to Ukraine, the moment the Ukrainian army takes control of them; those are part of the Ukrainian army. Whatever they are used for, they are used by the Ukrainian army. If they kill Russian soldiers, those soldiers have been killed by the Ukrainian.

But troops would remain part of their original army. Anything they do against the Russians, they would do as part of the Polish Army, guided by Polish officers, following the orders of the Polish government to which they still owe allegiance. It is a far more direct foreign implication.

The reverse also works: if the Russians destroy a tank provided by the Polish, they still have attacked just an Ukrainian tank and not a Polish one. But if they bomb a Polish company, the casualties would be Polish soldiers, not Ukrainian.

So, while the intent of both sending materiel and troops is the same and the effects may be sometimes similar, it changes the nature of the conflict as it means direct combat between the countries giving support and Russia.

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    "But troops would remain part of their original army." China disagreed in Korea. See my comments under o.m.'s answer. And what the USSR did in Korea, sending top of the line fighter jets (of then) with pilots, translated to modern times would be like the US sending F-22 squadrons manned by US pilots and pretending they are Ukrainian on some technicality (like giving dual citizenship or something). Sep 22, 2022 at 2:16
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    @FIzz I am not sure that the US necessarily bought the claim. It just couldn't realistically counter it because the US hadn't recognized China until 1979. PRC wasn't even a member of the UN at the time. It wasn't as if the US could summon PRC's ambassador to complain.
    – wrod
    Sep 22, 2022 at 2:28
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    @Fizz yeah but they pretended for those fighter pilots to be volunteers. And even if that pretense was paper thin, calling it out would likely lead to full out US-Soviet war, so the west pretended to buy this very obvious lie
    – Hobbamok
    Sep 22, 2022 at 10:32
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    en.wikipedia.org/wiki/…: "Soviet pilots wore Chinese uniforms when flying, whilst rules were prescribed to stop Soviet pilots flying near the coast or front lines (where they might be captured if shot down) and from speaking Russian on the aircraft radio. All aircraft flown carried Chinese or North Korean markings.[16] When not flying, for reasons of ethnicity, on the ground Soviet pilots 'played' the roles of Soviet commercial travellers rather than Chinese or North Korean soldiers. " They actually tried their best faking it
    – Hobbamok
    Sep 22, 2022 at 10:35
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    @Hobbamok Oh, sorry, I got what you said wrong. I thought that by "changing ownership" you meant to change allegiance and go working for the enemy, not transfer "ownership" to an ally. Sep 25, 2022 at 13:22

"Escalation" is mostly a red herring.

The big difference between sending weapons and sending troops to an ongoing war is that a dead soldier has a much larger political cost than a destroyed rocket launcher. Simple as that.

The same works in reverse. Having your troops killed by american soldiers is (politically) something else than having your troops killed by american weapons.

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    I don’t quite understand why getting a killed by an American rocket is supposed to be better than getting killed by an American firing a rifle? Sep 21, 2022 at 12:28
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    Because it's not an American Rocket fired by an American Rocket man that was made in America. It's Ukrainian Rocket fired by a Ukrainian Rocket man... MADE IN AMERICA!
    – hszmv
    Sep 21, 2022 at 12:49
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    @JonathanReez because when you get shot, you blame the person who did the shooting, not the one who made the gun. The weapons may have been sent from the US, but it is still Ukranians using them.
    – Seth R
    Sep 21, 2022 at 21:45
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    @JonathanReez, most weapons aren't made by the country that fired them. For anything more sophisticated than small-arms ammunition, local production is the exception, not the rule.
    – Mark
    Sep 22, 2022 at 0:28
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    @JonathanReez then they would be putting their own people in harm's way in defense of a foreign nation, which has its own political implications (especially back home). Besides, to my knowledge, Ukraine isn't asking for that. They have the people, they just want weapons. It has happened before though; for example, the Flying Tigers squadron was sent to fight Japan on behalf of China in 1941 before the US and Japan went to war directly.
    – Seth R
    Sep 22, 2022 at 14:18

International law is mostly based on precedent.

  • There is the precedent that selling arms is not, by itself, an act of war. This was e.g. supported by cash and carry during the early phases of World War II, when the US was not yet a belligerent. There were other, earlier precedents that neutrals may not sell arms in the Alabama Claims, so it is not completely clear cut, but recent precedent seems to indicate that selling arms to a belligerent is not an act of aggression. (It will be seen as unfriendly.)
  • There is a precedent that sending troops which do fight under the flag of the sending country is an act of war. It is a bit less clear how to treat large numbers of volunteers.

Regardless of law, there is something of an understanding that one does not push a nuclear power beyond their reasonable red lines. Those red lines are not necessarily based in international law, they are based in power politics. When the Soviet Union deployed nukes to Cuba, that almost triggered WWIII. Not because basing nuclear missiles in Cuba is fundamentally different from basing nuclear missiles in Turkey or the UK, but because it represented a change in the political balance that was unacceptable to the US.

The obvious problem with this realpolitik view is that it may allow nuclear powers to "get away with" unjustified actions, simply because nobody is willing to start a world war over them (compare the stability-instability paradox).

Where exactly these red lines are is a political bargain, with the mutual understanding driven in part by the diplomatic declarations of both sides.

  • Russia is trying to establish that any strike on Russia (including annexed territories) and any delivery of weapons capable of deep strikes is crossing a red line. Those are two different issues, by the way.
  • The West is not accepting the full claim of the Russian red line, but it has been reluctant to deliver such things as Western-made tanks and IFVs, long-range missiles, or combat aircraft. It has been delivering Soviet-made tanks and Western-made rocket and tube artillery.

The West wants Putin to be defeated, but it does not want him to panic. Those two goals may be mutually incompatible, so what the West does may be characterized as not letting Putin win, which is slightly different from him being defeated.

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    The whole Chinese army in Korea (supposedly 780,000 troops at its peak), run by PLA generals, counted itself as PVA. Including troop rotations, one Australian source says "2,200,000 Chinese served in Korea". Sep 21, 2022 at 16:35
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    And then there were the Soviet volunteer pilots somewhat better disguised though. Sep 21, 2022 at 16:44
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    @Trilarion, that might be lend-lease. At the time, it was far from certain that the UK could ever pay.
    – o.m.
    Sep 22, 2022 at 4:10
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    @o.m. I think that it is certain here that Ukraine can never pay for the assistance. With all the devastation of Ukrainian land going on the weapon deliveries are 99% a gift, which is fine by me but far from only an economic transaction. Sep 22, 2022 at 5:17
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    The initial weapon deliveries from the West to Ukraine were mostly Soviet-made but by now it also includes modern Western-made anti-tank-missiles and mobile artillery (which is essentially a tank with less armor and more range). There are no aircraft but one could argue that these would be useless without extensive training.
    – quarague
    Sep 22, 2022 at 7:11

Help of the western countries to Ukraine seems moderated by multiple barriers. HIMARS reaching 92 km are okay but ATACAMS reaching 300 km are not. Old tanks of 1970 year design are okay but the modern Leopard 2 for a long time were not, now okay, the things change. Drones and old Soviet aircraft are okay but modern military aircraft are not. Striking Russian munition depot in Ukraine with American rockets is okay, striking the same depot in Russian territory across the border is not. Lots of various economic sanctions are okay but using up the seized bank assets belonging to Russia state is not. Calling Vladimir Putin a war criminal that "should not remain in power" is okay, but naming Russia a terrorist state would be too insulting.

It is not clear how are these barriers established but the goal is probably to moderate the actual escalation of the conflict. They indeed look like some "hidden contracts": even if Russia declares they do not tolerate any intervention at all, they actually accept some within these limits. Sending troops currently belongs to barriers EU and USA opt not to cross.

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    Very nice examples. Could you maybe explain or link to a bit more information about "hidden contracts"? How could they possibly have been made here? Somebody must have decided which kind of support is ok and which not. Sep 21, 2022 at 15:59
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    @Trilarion: I doubt there were any explicit negotiations. The US probably went by how loud the Russian diplomats publicly protested against one system vs another. E.g. they said a lot more about HIMARS than about other stuff. So the US sent a rather limited number (about as many as Taiwan has and a fraction of what the US sold to Romania, for example--in terms of launchers at least. Getting data on HIMARS ammo sent/sold to these three is rather difficult.) Sep 22, 2022 at 2:26
  • The points you mentioned are why doubts have been risen in this question.
    – Gary 2
    Sep 22, 2022 at 15:49
  • I think that another concern about why one should not send modern Leopard 2 tanks: they might be captured and reverse engineered by Russia.
    – Tangurena
    Sep 22, 2022 at 20:42
  • A lot of this list has a very clear line drawn between each side as to why it is on each side. On one side you have primarily defensive options. On the other side, significantly more offensive options. Regarding calling him a criminal vs terrorist, because what is left out of the discussion is the legal implication. Naming Russia a state sponsor of terrorism changes US policy towards Russia. This would be a dramatic deviation from the US acting in step with the EU and other allies.
    – David S
    Sep 23, 2022 at 18:00

When soldiers of country X are tasked * with killing soldiers of country Y, there is one generally accepted word for it: War, between X and Y.

In contrast, when country X "only" supports forces engaged in a war with country Y, country X is not considered at war with Y.

Let's take some examples:


Russian and China support North Vietnam, fighting the USA. At war: North Vietnam vs USA + South Vietnam.

Afghanistan 80s

The USA + Pakistan support the Afghan rebellion against the USSR. At war: USSR vs Afghanistan rebels

South Korea, first phase.

Russia and China support North Korea vs South Korea and USA. At war: N Korea vs S Korea + USA.

South Korea, second phase.

China intervenes in North Korea vs South Korea and USA. The "war" state vs China is problematic and intentionally kept limited by the US, but Mac Arthur does not see it that way and loses his job for it.

Note that 1950s China is not nuclear which probably contributed to Mac Arthur's rather cavalier attitude.

At war: N Korea and arguably China vs. S Korea + USA.

Bottom line: there is a huge difference, historically, and that includes Cold War conflicts involving both Russia and the USA, between being an active belligerent and providing support. Both NATO and the Warsaw Pact took great care not to put their troops into direct conflict, even though both at times provided ample material support against the other.

Let's keep it that way.

* as opposed to cases where either there are accidental deaths or there is a localized, unplanned, incident leading to deaths.

  • "when country X "only" supports forces engaged in a war with country Y, country X is not considered at war with Y." Probably there are people that are seeing this differently. In this case here it would be sufficient if some Russians (e.g. Putin) see it differently. If he considers it to be at war it might not matter much what others think about it. Sep 21, 2022 at 19:58
  • It could also be called just a "special military operation" instead of war? Sep 21, 2022 at 22:03
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    @Trilarion whatever Putin thinks, or claims, he's not at war with NATO until he attacks NATO. His move, end of story. Sep 22, 2022 at 0:25
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    With Korea, the legal status was a bit more complicated: it was technically the UN on the S. Korean side, even though in practice it was 90% US troops.
    – Zeus
    Sep 22, 2022 at 5:33
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    In contrast, Bangladesh liberation resulted an war between India and Pakistan
    – Gary 2
    Sep 22, 2022 at 15:52

Many good answers are here, indeed. However, I believe that two key factors are not covered yet:

What’s the difference between sending a HIMARS launcher and sending a battalion of troops?

A battalion of troops implies a battalion of their spouses, 2 battalions of their kids, and 2-4 battalions of their elderly parents.

Even though these brave people may have volunteered to go risk their lives (contrary to just receiving the order), supporting their families would be a responsibility of their governments in case if anything happens with their lives or health. This always seems a hard decision for any government that cares of their people.
Human's life is the ultimate goal in the Western world.

Also, if losses actually occur, russian agents could try inflating social unrest in Western countries that even could overthrow the government. Just like they did it before:

Russian GRU defector Stanislav Lunev said in his autobiography that "the GRU and the KGB helped to fund just about every antiwar movement and organization in America and abroad," and that during the Vietnam War the USSR gave $1 billion to American anti-war movements, more than it gave to the VietCong, although he does not identify any organisation by name. Lunev described this as a "hugely successful campaign and well worth the cost". — Wikipedia

Ukraine has enough motivated people. Ukraine needs weaponry.

Unlike pictures you might have seen today on Russia (young people trying to evade mobilization), Ukraine has sufficient number of motivated young men and women who are ready to fight and who voluntarily go to the Armed Forces.

Here are queues at Military Commissariats in Rivne city on the first days of the full-scale invasion, circa 28/Feb/2022 (source)

Queues to Military Commissariat, Feb/2022

Many Ukrainian politicians also stress that Ukraine needs weapons:

Poroshenko: 'For peace we need three things: weapons, weapons, weapons'Deutsche Welle

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    About the last paragraph: there is a huge propaganda campaign going on from both sides. Just as easily as you pointed at some young Russians fleeing from mobilization and a picture of a couple dozen Ukrainians eager to enlist, some could point at young Ukrainian men fleeing the country and young Russians eager to enlist (including ethnic Russians living in Ukraine joining the separatists). Therefore, this is anecdotal evidence at best.
    – vsz
    Sep 22, 2022 at 8:39
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    @vsz It's hardly the same thing to compare people fleeing Ukraine because they feared it was about to be over-run, with Russians fleeing forced conscription. The press in Ukraine is reasonably free, yet we don't hear of them trawling through their gaols looking for volunteers either.
    – MikeB
    Sep 22, 2022 at 8:44
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    @MikeBrockington : I've seen and heard of many cases of bribing border guards to leave the country despite being eligible for conscription (living in a neighboring country, one might see and hear more things than which are widely reported).
    – vsz
    Sep 22, 2022 at 10:25
  • @vsz I agree that there is a huge russian propaganda trying to convince us about the equivalence between Ukrainians who are fleeing from devastated towns and russians who supported the war since 2014 and now realized that the war came back home on Russia. There is no evidence to consider the two situations equivalent yet, but I like your idea that someday it would become, indeed, equivalent for russian towns, too. :-) Sep 22, 2022 at 10:32
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    It should be also mentioned that Rivne, like the whole western part of Ukraine is a stronghold of ukrainian nationalists and suporters of both maidan revolutions. In that regions there are defenetly many motivated people who want to kill some russians, for which they are using a more abusive term "moskali". But that western regions are not representing the whole Ukraine and like @vsz said there are many young man triing to escape conscription in Ukraine.
    – convert
    Sep 22, 2022 at 11:48

Sending weapons and equipment is at heart a political/economic transaction. Nations send weapons to each other regularly, whether or not there is a current conflict. Sometimes armaments are bought by a state trying to shore up its military; other times they are offered to satisfy the security interests of the providing state. These kinds of deals can be controversial politically, but they are usually regarded as normal international transactions.

By contrast, sending in troops (aside from 'military aides') or firing long-range weaponry into combat areas usually signals that a nation is involving itself in a conflict directly, either as an act of war or as an emergency interdiction. The nation then becomes a combatant, and as such its troops, ships, bases, supply lines, and military production facilities become valid military targets. That creates the opportunity for major escalation.

Not to put too fine a point on it, but so long as Americans and Europeans don't shoot at Russian targets directly, Russians are constrained not to shoot directly at American and European targets. We can supply the Ukrainians with materials to fight their own war against Russia, but taking part in that war would open the door to Russian retaliation.

  • "...taking part in that war..." Even if sending weapons would only be an economic transaction, one could still regard the senders of weapons as a party taking part in the war. It all hinges on the definition of what taking part in a war actually means. For example there certainly is also a quantitative element. What if only a single NATO soldier would be sent (or two or three). Would anyone care? But with 500, people would care, so there must be a threshold somewhere. And that threshold would be defined by Russia. They could retaliate at any time for any reason, if they wanted to. Sep 21, 2022 at 17:40
  • Since you write good answers often, you can include why Russia warned the US against sending Longer Range weapons.. That would be a great addition to your answer.
    – Gary 2
    Sep 22, 2022 at 16:01
  • @Gary2: Well, the simple answer to that is that Russia doesn't want Ukrainian forces to extend their reach and attack supply and logistics in Russia or the Crimea. I assume the argument would be that giving Ukraine that ability would change the nature of the war in a way tantamount to direct involvement, but since Ukraine has already reached into Russia and the Crimea to hit depot and bases, I'm not sure how much water that logic would hold. But 'red line' talk is usually a measure of desperation; a way of negotiating boundaries to a conflict. I'm not sure it's really germane. Sep 23, 2022 at 5:08
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    @Trilarion: This may seem counterintuitive, but war (like all international relations) is essentially anarchic, and in anarchic contexts people invariable become highly dependent on collective norms and values. Nations and leaders need other nations to be basically predictable (because the alternative is quite literally Hobbesian hell), and so they try hard to stick to collective norms and values themselves. Yes, Russia could make expedient decisions on arbitrary thresholds, But doing so would be (pun intended) Russian roulette. Sep 23, 2022 at 5:24
  • @TedWrigley I'm perfectly fine with saying that by tradition sending arms is okay and sending personnel is not as long as we also say that in principle the responsibility is always shared really from a moral point of view. Deep down we should not make the mistake and think that sending arms is the same as sending medical supplies. Many answers to this question seem to make that mistake in my opinion. Sep 23, 2022 at 5:57

World Politics is complicated, but in the end there is no final law or arbiter. It's just what the head of state decides and maybe what the population thinks of it. Whether something is considered "fair" or "right" is shaped by the laws we live by in our personal lives.

Compare it to existing, accepted laws in most countries around the world, certainly Russia, Ukraine and any arms supplier, lets say the US, UK or Germany:

If a man gives you 100$ and in exchange you give him a knife, when they subsequently murder their wife with it, that is not the fault of the seller of the knife.

If a man gives you 100$ and in exchange you murder their wife, that is called being a contract killer, and it's illegal, as is hiring a contract killer in the first place.

So to summarize, selling goods means you are not responsible what happens with the goods afterwards. Selling services? You are responsible for that service. You cannot just claim that you only did that because you were paid for it. That does not absolve you of any crimes.

War is nothing but murder at scale. Supplying the weapons still means the other guy (or country or nation) is responsible. Supplying the actual service of killing enemies? You are in on it.

As a comparison, when the headlines broke that Russia bought ammunition from North Korea, nobody suggested that North Korea would become a party in the war. Not any more than if they had sold toilet paper or socks.

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    "International Law" may be a little more complex to enforce than National Laws, but things like the Geneva Convention do exist, and are (reasonably) clearly written.
    – MikeB
    Sep 22, 2022 at 8:48
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    Analogies sometimes do not get one very far. Soldiers for example do kill, but are usually not regarded as murderers and put into prison. Often they even argue that they are not responsible for their actions, were just following orders, that they are a bit like weapons. Maybe responsibility must be shared in the end by everyone who are involved, even remotely. Or even by those who didn't do anything. Sep 22, 2022 at 9:18
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    If a man gives you $100 for a knife to murder his wife with, and you know this, you're probably still going to be on the hook for "accessory to murder", which kinda breaks the analogy here.
    – Erik
    Sep 22, 2022 at 11:15
  • @Erik: technically speaking some countries do hold others to that standard by imposing certain sanctions. But others do not do that. So there is sometimes punishment for being "accessory to war". Perhaps fittingly, when this punishment exists, it's usually economic rather than military. And yeah, just like selling a gun to private person, sending weapons for "self defense" rather than aggression is viewed differently, although countries don't always agree who the aggressor is. "War is nothing but murder at scale" sounds cool, but if I say "self-defense is murder", what do you say, nvoigt? Apr 2, 2023 at 1:34
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    @Fizz I would say many things that the US considers self-defense are indeed considered murder where I live. It is a matter of perspective.
    – nvoigt
    Apr 2, 2023 at 6:23

Military equipment is property whilst military personnel are men. There is a fundamental distinction. It's the same difference in criminal law that distinguishes damage to property from murder.

Sending military equipment is a way of showing support without escalating the conflict more widely.

  • Military personel are humans/people, not just men, these days. :)
    – Erik
    Sep 23, 2022 at 8:30
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    @Erik Men works to define humans/people. One of the definitions of the root word "man" that men is plural of is a member of the species, or human/person.
    – David S
    Sep 23, 2022 at 18:19
  • Good point. Slaves from a third party country would not make that country a war party since they are property of one of the other parties. Sep 24, 2022 at 14:11

The "trivially true", but probably unsatisfying answer, is simply "because the relevant parties agreed that to be the case".

The rest are just narratives that the relevant parties agree or don't agree to use as an excuse.

The thing is "international law" behaves a lot different from what an individual might perceive "the law" to be. For example from the level of an individual, there is one or several super structures that: make law, enforce law and pass judgement.

When it comes to international relations there is no such thing. There is no (official) world government, no world police and no world court. There is something of a mutual anarchy (in the sense that there is no ruler). Sure countries can agree to have laws, courts and declare things crimes; and all of that is happening. But there's no obligation for anyone to accept any of the laws being passed, nor is there any dedicated institution that is able to penalize violating the law. Like with the laws and agreements those judgements might be passed but it's upon the perpetrator to accept them.

So what this boils down to is a complex web of reputation, agreements and powers.

Sure a perpetrator could technically say "laws don't apply to me", but practically that might mean that they are seen as unreliable and cut off from international trade and beneficial agreements or that other countries decide to go to war with them as they violate their interests and that further different countries will see that as a "just war" and supply them or remain neutral. So while most of these agreements are just as binding as you let agree to them being binding, they nevertheless posses some binding nature due to the fact that it would severely damage your reputation and international standing if you'd violate them and the more interconnected things get the more unlikely it seems to be for one country to opt out and just flip off every other country.

Now with respect to what constitutes an act of war. Same scenario, of course there are rules and regulations for what are good and not-so-good reasons to declare a "just war". But in effect a war is declared when a war is declared or when the first red line is crossed and that can be whenever one of the relevant parties says it is.

Objectively whether arms dealing counts as participation in war or not solely depends on the perspective. Like the arms dealer would obviously like to treat it as "just a job or just business as usual" and not get involved in all the nasty responsibilities and things that might hurt the bottom line. While if you are at the end that benefits from those deals you might agree with that neutrality not necessarily because you like it or actually agree with it, but because it's still better than not doing so, in the end it's still beneficial to you. While if you are on the receiving end of those arms you might argue more from the perspective of the arms dealer being part of the extended military supply line and declare it a legitimate military goal to cut the enemy off from that. And that's technically not wrong.

Practically though, unless you want to go for global tyranny, you still need to find agreement with your perspective in the camp of the other states that are currently not involved in the war, so it would make sense to frame your perspective as a universal doctrine. And in that case Russia wouldn't have a great case for itself, given that during the cold war there were lots of proxy wars where "just supplying one side with arms" was done by both sides and therefore explicitly declared NOT to be an active party in the war. Obviously that's a blatant lie, but if the relevant actors in that scenario agree on the lie, then it's de facto true for the sake of argument.

Because similarly to the cold war, the question isn't whether you COULD declare that an act of war (you always can whether that makes sense or not), but whether you actually WANT that.

And while Russia probably doesn't like other countries supplying Ukraine with weaponry, fighting an open war against all of those countries, at once, would mean a whole lot more weapons and soldiers on the battlefield. So the effect of that would be even worse. So it's a narrative they can use in their domestic propaganda, but internationally it probably only serves as a "red line". In the sense of "if you breach this line, we will attack you". Though declaring a red line in hindsight only works if you already want to attack and look for an excuse so if that's not the goal, you can only apply that to interventions that have no yet happened.

That being said there's still an intrinsic difference between supplying arms and supplying combatants and that is that the latter are human being and more specifically citizens and thus representatives of your country. So an attack on them either means an attack on your country, which technically either makes them moving "no shoot zones" or increases the threat of a necessity for war so massively that you might already call the deployment an act of war, or you'd have to basically disavow your citizens and the protection of your citizens from hostile foreign interference. So that's no longer between you and the respective enemy but between your country and it's citizens and as someone else noted for every battalion there's several battalions of relatives.

So while supplying arms and sending troops are probably both an involvement in combat, at least the former has an agreed upon plausible deniability while for the latter such a claim would become completely absurd (which is not to say that countries aren't willing to walk on these egg shells if they think they could do it). Like how Russia apparently send unmarked soldiers and disavowed relations to them in order to pretend an invasion is not an invasion. Though that has nothing to do with law, reason, logic or any of that sort and purely with the question what countries think they can get away with and with what other countries let them get away with.

  • Very balanced answer. As a tiny comment I would add that "an attack on them [human beings] either means an attack on your country" also goes the other way around. If a Russian soldier dies from a weapon delivered by the US for example, even if operated by a Ukrainian, then one could see this as an attack on Russia. But as you observe, Russia probably doesn't want to be in war with the US, so that simply gets ignored. Mar 31, 2023 at 13:46

I think it's a question of "leaving options on the table". It's a way the west can tell Russia "we'll tolerate your war of aggression against Ukraine but think carefully about how you conduct it because we have a lot more cards we could play".

Russia could deploy chemical, biological or nuclear weapons. I think they could have done more to attack Ukrainian ability to ship out grain, or start really going after civilian sea traffic in the Black Sea. So I think there's an argument that while the West isn't "all in" on this war, neither is Russia. And the West can possibly prevent Russia from going "all in" by the very fact that we aren't all in. "You don't cross that line and we won't cross this line" says each side to the other side.

I also think there's a strong argument to be made that really the war is not costing the West much, so the way we are conducting it now is practically free. You'll hear about the billions it's costing but the bottom line is we are mostly sending weapons we would never have used, and would have replaced within the stockpile over time anyway, so the cost of throwing an old Javelin into the dumpster is probably higher than the cost of handing it to the Ukrainians to go shoot it at some Russians instead. It comes out of the balance sheet as "cost of war" but I think you'd find "cost of not doing anything" would have been very similar. We aren't producing F-22s to give to Ukraine. The west is mostly giving them weapon systems that would otherwise just be collecting dust so the cost is a bit of a wash.

If the west sends troops, though, they will also send the latest and greatest top end equipment, and any losses then will be very real losses, both in lives and in brand new equipment that must be replaced.

The moment we send troops -- even, I think, a "no fly zone" -- is the moment a lot more cards go on the table and the closer both sides move to all out war.

  • "the west can tell Russia "we'll tolerate your war of aggression against Ukraine"" Officially this is not true. The West is not tolerating the war of aggression conducted by Russia. But you're right to say that they aren't all in. And this is very probably expression of how much they are in and how much they are out. I think that saying partly in is much more honest than declaring one taking part and another not. Sep 21, 2022 at 21:07
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    @Trilarion Yeah my argument would be that regardless of what they have actually said, the fact that no troops have been sent or that NATO is not presently carpet bombing Russian positions is evidence enough that they will tolerate Russian aggression, for some values of "tolerate". More to the point, it leaves them a lot of leverage, provided Russia actually believes in (or is not willing to risk) the west escalating to full involvement.
    – JamieB
    Sep 21, 2022 at 21:14
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    @Trilarion The West is tolerating Russian aggression in the sense that a group of people tolerates a bully beating on a little guy and the guy fights back. The underdog connected a hard punch with the bully and now the group is hanging back watching the fight, cheering for the kid, and passing him some brass knuckles. Its more a tolerating the aggression enough not to bloody your own fist on their face, but you're helping someone bloody that face. And as long as the bully keeps the gun holstered, the group will let the underdog win the fight on his own.
    – David S
    Sep 23, 2022 at 18:34
  • @DavidS In this case Ukraine isn't really winning. It's just not losing (yet). The war is fought on Ukrainian territory with Ukrainian civilians being in danger and Ukrainian soldiers giving their lives. Sure they get assistance from the west but that could be more. In that way it's a toleration. But it's not that the west wants Russia to wage that war. Maybe it's just a matter of wording. Sep 24, 2022 at 4:03

Letting Russia taste its own medicine

When the Russian army invaded Crimea and Donbass, RU government denied any involvement:

  • "Их там нет" (they aren't there) - the famous phrase of Vladimir Putin when asked about the Russian soldiers' presence.
  • "Форму можно купить в любом магазине" (anyone can buy Russian uniform) - from the same speech. The claim was that the Russian-speaking local people self-organized, captured arms from the Ukrainian army and rebelled against the Ukrainian government.

Later, Russia half-heartedly admitted helping the "rebels".

Even later, this claim was silently, but completely dropped as proofs about the opposite fact piled up.

An important point in the Russian propaganda is that Russia fights NATO and Ukraine is only a tiny facade. The propaganda pictures countless NATO instructors, officers and even ordinary soldiers in Ukraine. This point has its supporters and beleivers in Russia, in Ukraine and even in NATO countries.

Another important point in the same narrative is that the "West" holds Ukraine hostage and Ukraine soldiers are fighting against their own will. This is the whole idea of "liberating" Ukraine.

On the other hand, not fueling Russian propaganda is considered important by everyone (except, of course, Russians).

In a sense, the "red lines" that the western partners of Ukraine are reluctant to cross, are based on the perceptions of the general Russian population.

The propaganda is not omnipotent - even in Russia.

This precludes sending any military personnel in Ukraine (if there is at all a compelling reason to do so).


The first thing to note is that your premise is not entirely correct: The West cannot send (i.e., sell) "any forms of weapons (short of nuclear warheads) to Ukraine without causing the conflict to escalate beyond Ukraine’s border":

Russia has made clear that sending long range (even non-nuclear) weapons would make the sending country a war participant, presumably because those weapons would facilitate attacks on Russian territory that would otherwise have been impossible.

In short, everything that would presumably be traded in normal times does not in itself escalate the conflict. That is probably one of the reasons that there is a certain reluctance to send Western war tanks and other weapons systems that would imply that Ukraine is becoming integrated in the Western military infrastructure.

Russia has also made remarks that could be seen as hedging the option to e.g. bombard supply lines outside Ukraine if the weapons deliveries take on a quality that makes the seller seem like an active participant. Similar limits have been alluded to regarding reconnaissance and weapons training, especially training in Ukraine, even if the instructors do not participate in fights.

The second reason is that if we considered all countries who sold weapons used in conflicts parties to the respective conflicts, all major military powers would be or would have been parties to most modern conflicts on Earth, because selling weapons is such a profitable business that no major military power refrains from it, including Russia itself which is only surpassed in death dealings by the U.S. Making the countries who facilitate wars by providing the weapons party to the conflict would eliminate this opportunity for obscene profits, so nobody in their right mind would propose that.

The reason, on the other hand, that sending soldiers makes a country a party to a conflict is self-evident: Because the country now is a party to the conflict.


What’s the difference between sending a HIMARS launcher and sending a battalion of troops?

Just because nobody said it in other answers let's first say what it's not a difference in. It's not a difference in that it both would increase the military strength of the Ukrainian side resulting in higher loses on the Russian side. This battalion surely will not come unarmed and weapons will surely not be sent to civilians. So in any case arms and military personnel together result in an increased military force.

The main difference is what Guran states, involvement of people is raising much more emotional stakes than involvement of artificial devices even though from a factual perspective it hardly matters how exactly increased deadly force is achieved when it shows its impact. That's why one of these is typically considered war and the other one rather not.

By the way: the question of who is at war with whom or not is not so interesting either. Officially Russia isn't at war either. The more important question is what actions risk extending the scope of the combat zones. That's probably what actors are considering here. And if you commit servicemen, you cannot easily go back. For example, can you imagine Russia seeing the errors of their ways and retreat tomorrow? Neither can I.

  • Can you imagine? I can imagine.
    – Stančikas
    Sep 22, 2022 at 15:17
  • @Stančikas We will see. But I really don't think it will happen anytime soon. Sep 22, 2022 at 15:35

At the moment the West is deniing russian claims about war between Russia and NATO. Sending troops would be exactly this kind of war, also called World War 3. Such war would be very likely a nuclear one. Hope I was able to explain in brief the diference between a proxy war, we know from the time of the Cold War and World War 3.

Examples for proxy wars, mentioned befor are Vietnam and Afganistan. This countries were suplied with weapons by one of the opposing sides of Cold War to fight the other one.

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    @Trilarion, simplified but generally yes. It is a capitalist world -- selling weapons is viewed as being OK, the responsibility for the use is put on the buyer.
    – o.m.
    Sep 21, 2022 at 16:28
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    It wouldn't be a world war unless some other countries joined Russia. By itself, Russia is not a significant enough military power. Texas National Guard could probably go toe-to-toe with the Russian Federation's army.
    – wrod
    Sep 22, 2022 at 2:30
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    @wrod Troops involved in Ukraine now is just a small part of Russian army, so Texas National Guard destroing the whole Russian army is an idea from some Holywood movy. But the main point is that any nuclear war would be World War 3 as at will afect when not the whole then big part of the world.
    – convert
    Sep 22, 2022 at 10:25
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    @convert it's not the size of the army, but rather complete ineffectiveness of the Russian army that makes it weak. During the 6-day war the combined Arab armies outnumbered the Israeli forces by a factor of 2.5. And they had 3x as much equipment. They still lost. Training, logistics, and officer corp matters. The 1st US college math competition (Putnam) was b/n West Point (an officer school) and Harvard. West Point won. This should tell you something about the level of officer preparedness in the US.
    – wrod
    Sep 22, 2022 at 18:32
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    @wrod But USA have also fleed from Afganistan last year, does it also tell something about the level of officer preparedness in the US?
    – convert
    Sep 22, 2022 at 22:46

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