I came upon this (humorous) video where there are presented several incidents of the Swiss army accidentally marching into Liechtenstein due to bad map awareness and orientation. In the video they are called "accidental invasions". According to the video Switzerland even officially apologised for these incidents. In the comments there are even more anecdotes of the Swiss army accidentally ending up in other neighbouring countries like France and Italy. One comment goes as far as jokingly saying "So technically, Switzerland also accidentally invaded France with a one-man army" when a soldier going home fell asleep in a train and ended up in France.

These incidents happening during peace times between friendly countries with open borders between them, I found it off-putting at first to consider them invasions. But I guess this would have been a whole other story had other countries been involved.

Does this really count as an invasion? Or is it just a humorous device used in the video?

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    There was also that time when the UK accidentally invaded Spain... Commented Dec 20, 2021 at 9:17
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    Not watching the video, but it would probably depend if they had loaded weapons or if it was just someone in uniform who crossed over. Also some countries have agreements to allow troops to transit through them.
    – Stuart F
    Commented Dec 20, 2021 at 9:42
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    Obviously accidents happen. You hastily assemble thousands of 19-year-olds, tell them to prepare for the worst, and give them billions worth of complex equipment - there is bound to be confusion. Some common sense is necessary. There have been worse (sometimes deadly) unintentional provocations, under much more tense conditions, and we are all fortunately still here to talk about it.
    – Pete W
    Commented Dec 20, 2021 at 16:19
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    There was a similar incident recently with Poland "invading" Czechia, stationing troops in a church that they they mistakenly assumed was part of a Polish border village.
    – dan04
    Commented Dec 20, 2021 at 20:59
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    wired.com/2010/11/… "Last week, Nicaraguan troops crossed the border, took down a Costa Rican flag and defiantly raised their own flag on Costa Rican turf. But the troops’ commander, Eden Pastora, told a Costa Rican newspaper, La Nacion, that his invasion was not his fault, because Google Maps mistakenly said the territory belonged to Nicaragua. " This one is a much more interesting case. Commented Dec 20, 2021 at 23:18

6 Answers 6


It depends on what you mean by "invasion." To the best of my knowledge, there is no single treaty that offers a uniform, widely-accepted definition of this term in the context of international relations. The word is commonly understood to connote an act of war ("for conquest or plunder"). If there is no actual fighting, the whole incident is short-lived, and everything reverts to the status quo ante afterwards, then it is very difficult to characterize that as a "war."

On the other hand, these incidents cannot simply be dismissed as completely trivial. When armed forces, in whatever number, cross a border unlawfully, that is a violation of a country's sovereignty, and from a diplomatic perspective, both countries concerned have no choice but to take it seriously. This is why you will often see frantic diplomatic messages back and forth between the two countries: The country that was "invaded" needs to establish, on the record, that this sort of thing is Not OK™, and that they are prepared to defend their borders if necessary, and the country that did the "invading" needs to establish that it was a rare lapse rather than the normal way that their military operates. This narrative (i.e. "these scenarios are extremely rare, we take them seriously, and we're sure it won't happen again") works to both countries' advantage, and so these sorts of events tend to be resolved in relatively short order compared to other geopolitical conflicts. But if the countries already have a poor relationship, misunderstandings about the border can make things worse. It may even be done as an act of deliberate provocation, in hopes of getting the other country to overreact and waste geopolitical capital on a "minor" issue.

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    'cross a border unlawfully' Would it necessarily be unlawful? Switzerland and Liechtenstein are both in the Schengen zone, so people in general can cross the border freely; is there any clause in the Schengen agreement that says "except military personnel in uniform"? Commented Dec 20, 2021 at 20:31
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    @DanielHatten more than that, Switzerland and Liechtenstein were in an immigration and customs union for a very long time before they both joined the Schengen area, so the border between the two is more open than are their borders with any other country. But yes, in general, armed forces are not supposed to enter other countries without permission. They probably weren't breaking immigration laws but that doesn't mean they weren't breaking some other law.
    – phoog
    Commented Dec 20, 2021 at 21:22
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    The disputed China-India border, for example, has plenty of provocations including firefights. The US also routinely attempts to send ships and aircraft right next to other countries' borders, for example China. This may lead to things such as the a U2 and USS Pueblo being donated.
    – obscurans
    Commented Dec 20, 2021 at 21:56
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    @obscurans That 'firefights' is singular, an allegation and (from your quoted article): " ... if true, would be the first time in 45 years that shots had been fired there"
    – mcalex
    Commented Dec 21, 2021 at 7:23
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    For more details about Switzerland "invading" Liechtenstein (although the latter uses the currency, border patrol of the former): see "Incidents involving the Swiss military" on en.wikipedia.org/wiki/… My personal favorite quote is not any more on the Wiki but I think it was the Prince of Liechtenstein who said (about the 1992 incident, IIRC): "Nothing happened that cannot be solved by a discussion over a bottle of fine wine."
    – D. Kovács
    Commented Dec 21, 2021 at 10:06

It depends.

  • The defection of uniformed soldiers, even if armed and in groups, is clearly not an invasion. They are obviously acting without orders.
  • Various alliances have treaty agreements to permit transit or even deployments. Under NATO Status of Forces Agreements, military ID documents and marching orders replace the passport and visa.
  • There are treaty agreements regarding the transit of foreign warships through some waterways.
  • Navigational errors are generally considered "not an invasion," even if there are heated exchanges afterwards. Remember Gary Powers, who even admitted that he had acted under orders?

So the answer is "no, not always." The rest of NATO would have had to come to the aid of France.

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    The NATO treaty speaks of "armed attack." This seems a higher bar than "invasion." That is, it seems more reasonable to argue that armed soldiers crossing the frontier without violence is an "invasion" than that it is an "armed attack," though I would argue that in most cases it is neither.
    – phoog
    Commented Dec 20, 2021 at 12:15
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    Fair enough. It's not necessarily the case that one is easier to reach than the other of course; it's possible that there are invasions that are not armed attacks as well as armed attacks that are not invasions (as you have demonstrated). Mainly, however, I would note that even if the accidental incursion of an armed Swiss military force into French territory were held to trigger the provisions of the treaty, it's difficult to see what action would be required to "come to France's aid" after the Swiss realized their mistake and returned to Switzerland.
    – phoog
    Commented Dec 20, 2021 at 13:13
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    @o.m. Yes, but 'under orders and in uniform' == invasion, whereas 'under orders and in civvies' == espionage. OP asked about invasion. Gary was working for the CIA and WAS charged (and convicted) of espionage. He was doing recon, not fighting.
    – mcalex
    Commented Dec 21, 2021 at 9:47
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    @o.m. it's not fiction; the CIA is legally a civilian organization. The use of "civilian" to describe, for example, people who aren't part of a police force, does not comport with the the meaning of the term in the international law of war. In that context, police forces are also civilian.
    – phoog
    Commented Dec 21, 2021 at 10:58
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    @o.m. That's completely different. That the US CIA was conducting aerial surveillance of the Soviet Union was openly acknowledged, at least within a couple of years. That CIA and KGB officers were operating in each other's territory was also widely known. Attempts to claim that the flight was a lost weather plane were abandoned when it became apparent that they were not tenable. Conversely, nobody is abandoning the untenable claims about little green men or so-called volunteers, nor is the source of their command and control obvious.
    – phoog
    Commented Dec 21, 2021 at 14:25

I guess it all depends on how the invaded country wants to see it. For example when the Germany army used a road on Dutch territory to invade Belgium in WW1, the Dutch government (wisely) decided to ignore this fact and managed to keep the Netherlands neutral this way.

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    This is a non-trivial point. Generally speaking, an invasion or action isn't an invasion of act or war until the "victim" chooses to characterize it in that fashion.
    – ohwilleke
    Commented Dec 21, 2021 at 2:14

There was an infamous case in 2018 where 2 Greek officers crossed into Turkey, by mistake, and they spent 6 months in a Turkish prison.

See https://en.wikipedia.org/wiki/Greek%E2%80%93Turkish_relations#Soldiers'_arrest

According to the wiki article, the

Turkish courts [had] ordered their detention on suspicion of illegal entry and attempted military espionage

So even between two extremely hostile countries, it wasn't considered an invasion.

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    I thought that under international law, being in uniform is a defense against charges of espionage. Commented Dec 21, 2021 at 0:50
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    But no one considered it an "invasion."
    – ohwilleke
    Commented Dec 21, 2021 at 2:13
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    @Acccumulation: Not sure how closely international law is followed by Turkey, but I guess that's why they were eventually released. They still spent half a year in Turkish prison though.
    – user000001
    Commented Dec 21, 2021 at 9:23
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    @Accumulation being in uniform allows one to qualify for the protections of the Geneva conventions in a time of war; without those protections, one is more likely to be "shot as a spy," as the usual saying goes. But being in uniform is certainly no defense against normal espionage charges. Imagine someone taking clandestine photographs of a secret military base when there's no war going on Would it make sense for the law only to penalize this conduct only if the person is not wearing a military uniform?.
    – phoog
    Commented Dec 21, 2021 at 14:32

Nope. "Invading" is going into a country with the goal of parenting it in some way. It doesn't matter if they wear their PJs or Rugby-gear, if their higher-ups command them to seize control of the state they are going into, that's invasion. How the hosting country chooses to see it is a different story, of-course.

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    >It doesn't matter if they wear their PJs or Rugby-gear,... I think it matters very much if they are captured. If they are captured wearing uniforms they would normally be entitled to be treated as POWs. If they are in civvies the invaded country can summarily execute them. Of course if they are not captured, and they manage to win the war, then you are right: they can do as they please. Commented Dec 21, 2021 at 2:40
  • @SimonCrase I don't think there's a provision in international law that justifies executing ununiformed members of a foreign military for merely wandering into another country. Your comment seems to rely on the word 'invaded' but it's not clear what that means. Indeed, that's what the question asks about. Further note that the Geneva Conventions apply in the context of armed conflicts. If there's no armed conflict (which there wasn't in the example in question) then all of that seems irrelevant.
    – JJJ
    Commented Dec 27, 2021 at 11:32
  • "Your comment seems to rely on the word 'invaded' but it's not clear what that means." Maybe because my comment was in response to an answer that used the word "invasion" twice. Commented Dec 27, 2021 at 20:50

In september 2021, military men from Bolivia entered to chilean territory to steal cars. They were detained by chilean police and sent to the judge. The chilean judge sent them to prision for steal, carrying guns and ammo.
So, military men carrying guns and using them in a foreign country are considered common crimes.

Chile and Bolivia does not have ambassadors since several decades. So they are not precisely friendly.


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