NATO countries are very careful to not attack Russian forces in Ukraine. The main rationale given for this is "Russia has nuclear weapons. Attacking Russian forces might lead to a nuclear war."

Similarly, it seems that Russia is very careful to not attack NATO countries. One excuse for attacking Ukraine is that "it wants to join NATO", but other countries - which already jointed NATO - are not attacked. Probably, the rationale is similar: "NATO countries have nuclear weapons. Attacking them might lead to a nuclear war".

Now, suppose the USA (or another NATO member) invades Ukraine from the west, and occupies all the territories not currently occupied by Russian forces. Now, apparently, there is a symmetric condition: two occupying forces, both have nuclear weapons, both are careful to not attack each other in order to avoid a nuclear war. So the hot war will end. For Ukraine, this situation will be much better than being entirely occupied by Russian forces, so they might agree to this plan.

Is this consideration correct? If not, then where exactly the symmetry breaks?

NOTE: I understand that my "idea" is probably too naive, I just want to understand where exactly it fails. Why is this not a symmetric situation?

  • 4
    I see no difference between your idea and NATO/US trips entering Ukraine as allies of the current Ukrainian government
    – SJuan76
    Mar 17, 2022 at 18:11
  • 1
    It also doesn't "fix" the situation all that much from the, long term, POV of Ukraine if Russia remains in control of what they have, rather than heading back home. That's a partition, which no state would consider lightly. So, lots of risk, limited upside. Where Ukraine would benefit, short term, is from having NATO come in on their side. Mar 17, 2022 at 18:51
  • "Why is this not a symmetric situation?" Because it never is symmetric. The US is not that desperate than Russia and Ukraine is not that close to the US than to Russia and Biden is not Putin and many more things aren't equal. Mar 17, 2022 at 20:38
  • Such an occupation, clearly intended to counter Russia, may by itself trigger a nuclear war. An interesting relevant example is occupation of Lebanon by Israel and Syria (though it didn't risk a nuclear war).
    – Roger V.
    Mar 18, 2022 at 9:35
  • Any answer will be speculative, of course, but I'd point out that Putin threatened "consequences they have never seen" to anyone who interferes in the operation, so it's possible such NATO action will lead to nuclear war.
    – Allure
    Mar 18, 2022 at 13:29

3 Answers 3


I answered a slightly different question with

[...] There are a number of requests and suggestions which come down to let's have a war between the West and Russia, so Ukraine doesn't stand alone. They include

  • immediate NATO membership,
  • immediate EU membership,
  • NATO air forces over Ukraine to enforce a no-fly zone,
  • NATO air defense forces in Ukraine to enforce a no-fly zone,
  • NATO ground forces in Ukraine to protect people.

[...] So the proposal comes down to a war between the NATO members and Russia. An entirely understandable request from Ukraine, who are in the war, but countries not yet at war with a major nuclear power might hesitate a bit. [...]

I did put NATO troops defending Ukraine on the list. It doesn't really matter under which label those troops come, as long as there is a significant number of combat troops.

Elsewhere I answered

One can debate going to war over Ukraine, but please do it with open eyes.

  • 1
    If NATO puts troops in Western Ukraine, it will be Russia's choice to start a war with NATO. It would not be NATO starting a war against Russia. Mar 17, 2022 at 19:44
  • Why is the situation not symmetric? Mar 17, 2022 at 20:43
  • @ErelSegal-Halevi, because Putin is willing to risk a war, and NATO isn't. This is not just about international law, but also about not pushing nuclear-armed powers into a desperate situation.
    – o.m.
    Mar 18, 2022 at 5:27
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    @Acccumulation: I disagree. As long as all NATO countries do is aiding and supplying Ukraine, they are not engaging Russian troops. There are defined borders that both sides could decide not to cross. If, however, NATO would move troops into Ukraine, and they meet the Russian advance, it would have been NATO's decision to engage, without a border or even an agreed cease-fire line. But even then it would not be "Russia starting a war with NATO", because article 5 is about self-defense. Indivisdual NATO countries could decide to engage as well, but it would be up to them... (t.b.c.)
    – DevSolar
    Mar 18, 2022 at 12:02
  • 1
    @Accumulation You can't start "a war with NATO" unless you are attacking a NATO member's territory, because NATO members are not obliged to support each other in offensive operations. And troops moving up to the frontline of a shooting war is an offensive operation. Demanding that the Russians ask nicely for nationality before e.g. firing artillery or dropping a bomb or shooting at a shape in the dark they identified as "not friendly" and going "or else" is just unrealistic. NATO moving up to the frontline would be NATO deciding to engage.
    – DevSolar
    Mar 18, 2022 at 19:46

It is a plausible scenario. NATO would not want to share a border with potential Russian military client state. They would need a buffer zone and that may lead to the partition of Ukraine (google for many maps) and may eventually end the war.

It's hard to tell how probable that is.

In this case, NATO forces would enter Ukraine and will probably have under-the-table agreement with Russia about that.


Probably not because Russian troops surround some large Ukrainian cities. According to UK's MoD as of this morning

Kharkiv, Chernihiv, Sumy and Mariupol remain encircled by Russian forces and have experienced heavy shelling.

There would be no way for Western troops to peacefully get in and establish the equivalent of West Berlin(s) in these areas, unless the Russians agreed to that.

So war/sieges will likely continue in more than half of the country.

As for how Putin would react militarily to NATO troops crossing Ukraine's border that's very much open to speculation, but it would certainly help his narrative that Ukraine is a NATO puppet etc.

Also, your question is extremely hypothetical not only because the lack of NATO will to do such a thing, but also because Western NATO forces are present in quite low numbers (tens of thousands) in Eastern Europe, with barely 100 tanks or so. Eastern NATO members have militaries quite inferior to Russia's both qualitatively and quantitatively. It's quite uncertain they'd even be capable of a large scale peacekeeping operation, as Ukraine would require.

Flying NATO troops into Ukraine in sizeable numbers is most implausible because Russia can bombard airfields with cruise missiles etc. Assembling a credible NATO force on the ground in Eastern Europe will probably take months. See how long the preparations for Desert Storm took, for instance, or what the fuel requirements were.

Seeing the build-up Russia could pre-emptively invade Eastern Europe countries too; it has a direct border with the Baltic countries. Speaking of which, the scarcity of NATO ground forces facing Russia in that sector is a perennial discussion issue for Western planners and pundits alike.

  • The bad performance of Russian troops in Ukraine came as a shock to many observers. Are you sure that the East European forces are really qualitatively inferior?
    – o.m.
    Mar 17, 2022 at 18:28
  • @o.m.: yes: Romania has tanks that are basically T-55; Poland has less T-72s than Ukraine has etc. They recently got some F-16s but still use plenty of older Soviet aircraft as well (Mig-21s in Romania--one recently crashed). Moving troops forward is no easy task.
    – Fizz
    Mar 17, 2022 at 18:29
  • I seem to recall a quote about the 1991 Gulf War by an American general. Roughly "we would have won if we had had their gear, and they had had ours."
    – o.m.
    Mar 17, 2022 at 18:50
  • @o.m. I call BS on that: most Iraqi troops that fled did so after massive air bombardments. And those that stood their ground and died did so because they were outranged by Western tanks (better thermal imaging etc.) If Iraqis had B-2s with which to level the assembly areas, never mind Tel Aviv, the coalition would have probably never attacked. It would have been like Obama on Crimea: "they annexed it, we can't do much about it."
    – Fizz
    Mar 17, 2022 at 19:03

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