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Per title. E.g. right now the US has a mutual defense treaty with the Philippines and also with South Korea. If the Philippines and Korea go to war with each other, who is the US obligated to help?

I imagine this must have happened in history (making this perhaps better asked on the History SE), but I can't find any examples, and in that case this is likely the better place to ask. The closest example I found was US involvement in the Falklands war, but that never led anywhere because the US wasn't legally bound to assist either side:

At first glance, it appeared that the US had military treaty obligations to both parties in the war, bound to the UK as a member of the North Atlantic Treaty Organization (NATO) and to Argentina by the Inter-American Treaty of Reciprocal Assistance (the "Rio Pact"). However, the North Atlantic Treaty only obliges the signatories to give support if the attack occurs in Europe or North America north of the Tropic of Cancer, and the Rio Pact only obliges the US to intervene if one of the adherents to the treaty is attacked—the UK never attacked Argentina.

Allure
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    If it's 'mutual defence' the key will be who is the aggressor of course there is some leeway in how that is determined –  Oct 31 '19 at 13:27
  • "the UK never attacked Argentina": does Argentina agree with that statement? Or does the US treaty obligation to Argentina say anything explicit about disputed territory? @Displayname that comment sounds like the beginning of a good answer. – phoog Oct 31 '19 at 14:08
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    The tangle of military treaties is the reason that we went from a Serbian assassination of an Austro-Hungarian Duke to a World War that was largely blamed on Germany. The Web of honored treaties was so tangled that the exact progression from assasination to "War to End all Wars" is still not fully understood to this day. The entry of all great powers in Europe into the war turned what was likely a one year affair into a 4 year war (Austro-Hungary declared war on Serbia in 1914 and Serbia was defeated by 1915.). – hszmv Oct 31 '19 at 14:28
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    @phoog the US did not regard Britain as the aggressor as the US has never regarded the Falklands as part of Argentina. No LA nations went to war with the UK as would have been required under the Rio Pact, though some did express support. – gormadoc Oct 31 '19 at 21:25
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    You just choose one side. That one that is going to win. Vae victis, pacta non sunt semepr servanda. Italy in WW1 also just chose the side with a better promise of the booty. – Vladimir F Героям слава Oct 31 '19 at 21:50
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    @gormadoc the thing about multilateral treaties is that it usually doesn't matter what one party's interpretation is. – phoog Nov 01 '19 at 00:16
  • @gormadoc To be solely part of Argentina. It recognised the Falkland Islands as under joint British and Spanish sovereignty, and acknowledged that Argentina took the Spanish claim after independence. Argentina negotiated with Britain to start a new colony there (recognising the British claim to the islands), and then declared it to be solely Argentinian, which is what the USA never recognised. Except, the Argentinian-appointed / British-approved Governor of the island soon after declared the island to be independent of any external Government, and the Argentinian troops mutinied. – Chronocidal Nov 01 '19 at 13:03
  • @phoog but it does. There's nothing actually forcing any nation to comply with international treaties but upset relations, absent some country willing to use force or sanctions to get what they want. When it comes to the US, that means it's usually just upset relations and threatened sanctions. China is currently violating the 50 year agreement between themselves and the UK. Nobody outside China is really doing anything about it besides demonstrations. The UK's interpretation just doesn't really matter in making China comply. – gormadoc Nov 01 '19 at 14:07
  • @Chronocidal the US has never recognized Argentine sovereignty over the islands, which is different from previous Spanish claims to the islands. Argentina claimed a larger area than the US recognized. This is acknowledged in Williams v. Suffolk Insurance Company, a SC court case: "... seizure of the Harriet by the authority of the Buenos Ayrean government, ... at the Falkland Islands was illegal and contrary to the law of nations on account of the said islands' not being within the territorial sovereignty of the said Buenos Ayrean government ... " – gormadoc Nov 01 '19 at 14:14
  • @gormadoc sure, a country can interpret a treaty unilaterally, but then the country is no longer operating in compliance with the treaty, or at least the other parties to the treaty would be justified in taking that position. That's why I asked about Argentina's position with respect to the military activity in question and the Rio pact. I wasn't asking whether the US was actually obliged to support Argentina, only for Argentina's position on the question, or at least an analysis from the Argentine point of view, and whether the treaty itself had anything more specific to say about it. – phoog Nov 01 '19 at 14:39
  • If there's a regulatory entity, then they will make sure that this law can be re-interpreted in order not to make it unfair or controversial in case of ambiguity, but if there's no regulatory entity (and in case of total and all encompassing war there aren't) then the U.S can do how they please. The same issue can happen about war rules, they are just meaningless, since every mean can be used. – abdul Nov 01 '19 at 15:00
  • @phoog as far as I know, Argentina did not invoke the treaty during the British reconquest. Cuba pledged support beforehand but wasn't called upon during. From what I'm finding, criticisms of the US support for Britain during the war don't rest on the language of the treaty but on the spirit, and are mostly modern. – gormadoc Nov 01 '19 at 15:04
  • From my personal memory of the events, I recall that when the UK Task force was en route to the Falklands, the Argentinian government approached the US asking for satellite images of British fleet. I don't think they were obliged, however, and, in fact, the US went on to supply the British with rather useful intelligence - http://www.thespacereview.com/article/2258/1. – Oscar Bravo Nov 03 '19 at 10:54

6 Answers6

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Very smart people are still trying to figure this out.

Perhaps surprisingly, this is far from resolved, and is currently an ongoing topic of rigourous legal and political discussion.

A good starting point might be Valentin Jeutner's book Irresolvable Norm Conflicts in International Law, based on his doctoral thesis defended at Cambridge University in 2015, which is the latest in a recent series of monographs that address norm conflicts in international law.

A fairly-involved review of the book discusses this specific topic and its current unresolvedness:

Egypt is party to both the regional 1950 Joint Defence Treaty and the bilateral 1979 Peace Treaty with Israel. Under the Joint Defence Treaty, a multilateral military alliance treaty with members of the Arab League, Egypt is under an obligation to aid any state party to the treaty in the case of aggression against that state, whereas the 1979 Peace Treaty with Israel puts Egypt under an obligation to refrain from any direct or indirect use of force against Israel. Should Israel now use force against an Arab League state and should that state invoke the Joint Defence Treaty, Egypt might find itself facing two potentially conflicting treaty obligations: to aid the Arab League state through the use of force against Israel and to refrain from the use of force against Israel.

[...]

The court will need to exercise an interpretatory function, and the interpretation will probably hinge upon the concrete question submitted to it. Therefore, it might not actually come to interpret obligations that are in conflict with each other. In order for a court to issue a dilemmatic declaration in the sense that Jeutner proposes, it would need to be the state facing the conflicting obligations to submit the conflict to the court. This seems rather unlikely in contentious proceedings.

Roger
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    In such a situation, wouldn't the obligation from the later treaty simply override that from the former one (like with literally any set of laws with identical authority levels)? – Vikki Nov 01 '19 at 04:31
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    @Sean: No. If you and I make a deal that includes my selling you my car, and then Roger and I make a deal that includes my selling him my car, I can't just go back to you and say that my obligation to you has now been overridden by my obligation to Roger. Rather, my deal with you should have precluded me from making the conflicting deal with anyone else. – ruakh Nov 01 '19 at 06:05
  • @ruakh: Then why not simply have the preexisting treaty obligation override that from the later treaty? – Vikki Nov 01 '19 at 06:19
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    @Sean: For the same reason that crossing my fingers behind my back while "selling" my car doesn't mean that I get to keep both the money and the car. The 1979 Peace Treaty involved major concessions on Israel's part; Egypt's preexisting treaty obligations to other countries don't entitle it to accept those concessions from Israel while ignoring the promises it made in return. – ruakh Nov 01 '19 at 06:36
  • @ruakh: But you just said that those new promises couldn't override its preexisting treaty obligations; which one is it? You (or Egypt) can't have your cake and eat it too. – Vikki Nov 01 '19 at 06:56
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    @Sean International treaties don't always follow logic. There can be conflicting treaties with different parties without either superseding the other. Treaties can be ignored if they are inconvenient. Depending on the incident, it might lead to international sanctions and internal political backlash, but if there is reasonable cause, like such a conflict, people might just accept it. Treaties are in essence just statements of intent and while most tend to be turned into law through ratification, they can't force a country to act against it's wishes if it's willing to accept consequences. –  Nov 01 '19 at 08:04
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    @Sean You are restoring 3 cars (Red, Green, and Blue). You make a deal with ruakh to give him one of his choosing when you finish it, if he pays you for it now. You made the same deal with Roger. When later you finish the cars, you tell them - they then both send letters, arriving on the same day, asking for the Red car. Who gets it? Neither deal that you made contradicts the other, but the choices that ruakh and Roger made on how to apply the deal afterwards are mutually exclusive. (And, you have already spent the money restoring the cars, so you can't give it back) – Chronocidal Nov 01 '19 at 13:31
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    @Sean: "I can't have my cake and eat it too" is exactly the issue. I shouldn't have made two contradictory agreements with you and Roger. Having done so, I can't simply weasel out of my promise to one of you by saying it's overridden by my promise to the other. – ruakh Nov 01 '19 at 14:50
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    @Sean The comparison to laws in not reasonable. A later law can supersede an earlier law because laws don't bind legislatures to outside parties. In the case of a treaty, the entity that made the later treaty was itself bound to outside parties by the earlier treaties and could not agree to do something it had already agreed not to do. If I state my own policy twice, the later policy overrides the former. But if I make an agreement with Alice and then an agreement with Bob, I could not agree with Bob to do anything I agreed not to do with Alice because I already gave up my right to do it. – David Schwartz Nov 02 '19 at 04:52
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    @ruakh note that neither treaty specifically precludes other. They are not in conflict as treaties, but only if specific unforeseeable conditions arise. – Gnudiff Nov 02 '19 at 06:23
  • @Gnudiff: I'm not qualified to analyze the terms of the treaties -- my comments were just to help Sean understand why neither treaty can override the other -- but I'm surprised that you describe those conditions as "unforeseeable" in 1979. By that time, the Six-Day War had demonstrated that Israel was prepared to launch preemptive attacks if necessary; and much of the stage had already been set for the 1982 Lebanon War. – ruakh Nov 02 '19 at 06:58
  • @ruakh There may not have been any conflicts at the time - but the political majority may change (in all three countries), and a new agenda be set. – Baard Kopperud Nov 03 '19 at 13:35
  • @BaardKopperud: I'm sorry, I don't understand why you've directed your comment to me ; it doesn't seem to be a response to anything I wrote? – ruakh Nov 03 '19 at 16:28
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Most mutual defense treaties are very explicitly defense treaties. They cover the case where a third nation attacks one or both of the signatories. It is rather difficult for two countries to attack each other first. So the country which has a treaty with both has to see who was attacked and who did the attacking.

  • In theory, a straightforward matter of facts and international law (what is an act of war and what is a provocation short of war ...).
  • In practice, this judgement will be clouded by politics, and the treaty partner could deliberately take the wrong decision or get itself blinded by political bias.
  • A treaty partner of both might work to calm the situation instead of getting involved, too. Again a political decision.

For historical perspective, look at the various clashes between Greece and Turkey, both NATO members.

Of course there might be cases where a "defense" treaty also covers offensive action. While this example concerns just two parties, the relatively unconditional Imperial German support for Austria-Hungary is one of the contributing factors for the start of WWI.

o.m.
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  • It is rather difficult for two countries to attack each other first. It's quite conceivable for me though - for example, perhaps the Philippines has a mutual defense pact with Malaysia and South Korea has a mutual defense pact with Japan, Japan goes to war with Malaysia, and both Japan & Malaysia invoke the treaties. – Allure Nov 01 '19 at 00:43
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    @Allure which one performed the first act of war (Japan or Malaysia) on the other in your scenario? That tells you which is the aggressor and which is the defender. – Tim Nov 01 '19 at 01:30
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    @Tim right, but Korea and the Philippines would be at war without either of them being the aggressor. Their ally might have attacked, but not them. Roger's answer above gives a better example, as well. – Allure Nov 01 '19 at 01:39
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    @Allure oh you’re saying there’s a fifth country with a pact with both P and K? This is getting complex but I’d assume one follows the chain down? If J attacked then the new number 5 would side with M and P, and vice versa. – Tim Nov 01 '19 at 01:42
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    @Allure, chains of treaties are blamed for the tensions in the run-up to WWI. Austria has a quarrel with Serbia, and for that reason Germany violates Belgian neutrality to attack France? Completely logical if there is a tangled web of treaties .... – o.m. Nov 01 '19 at 05:50
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    It is rather difficult for two countries to attack each other first. — it is rather easy for two countries to accuse each other of attacking first, such as at the start of WW II or the Korean War. – gerrit Nov 01 '19 at 09:02
  • @gerrit To disambiguate, which of the several possible starts of WWII are you counting (I'm presuming the invasion of Poland)? – origimbo Nov 01 '19 at 13:14
  • @origimbo Yes, I mean the German invasion of Poland (I believe this is the most commonly chosen date for the start of WW II in Europe) – gerrit Nov 01 '19 at 13:29
  • @gerrit, that would be my second bullet point. Each nation in the chain of treaties has to decide if they acknowledge that the treaty is in effect. Removing this disambiguity is one reason why during the Cold War, there were US units right at the Iron Curtain. – o.m. Nov 01 '19 at 14:31
  • @gerrit I believe the more poignant example(s) are Russian. Both the war against Georgia and the Crimean affair was oblique and muffled to the point of being really difficult to discern any hostilities officially. Which means singling out the attacker or even that an attack had taken place - would have plausible deniability. Scary stuff. – Stian Nov 03 '19 at 09:03
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In your situation, assuming de-escalation didn't work, the country in the middle would do one thing, and one thing only: whatever is in their best interest.

The main signpost that helps political realism to find it's way through the landscape of international politics is the concept of interest defined in terms of power.

...

Intellectually the political realist maintains the autonomy of the political sphere, as the economist, the lawyer, the moralist maintains theirs. He think of interest defined as power as the economist thinks of interest in terms of wealth...The political realist asks "How does this policy affect the power of the nation?"

This could mean taking no side, taking a side that has longer upside potential, selling arms to both, or any myriad of policy positions. But these positions will not be based upon whatever is stated in some treaty.

All quotes from Politics Among Nations, Hans Morgenthau, sixth edition

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    This is probably the most realistic answer, judging from international examples. One of the latest examples (not explicitly a defense treaty, but covered similar topics) would be the major nuclear powers that signed the Budapest memorandum https://en.m.wikipedia.org/wiki/Budapest_Memorandum_on_Security_Assurances guaranteeing the territorial integrity of Ukraine. We know how that turned out. – Gnudiff Nov 02 '19 at 10:06
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A decision to adhere to a treaty is always a political decision.

It is a mistake to think about international treaties as if they were laws, because there is no international government with the mandate and capability to enforce them. If you and I make a contract, and I break it, you can go to court to make me honour it. There is no equivalent for international treaties. (Yes there are international courts, and the United Nations, but neither is in a position to enforce its decisions unless a majority of powerful nations has the political will to back them. Meaning it's still a political decision.)

Therefore each country decides if it will follow up with its treaty obligations when it believes it is in its interests to do so. That's not to say they look only at the short term convenience - most countries don't want to get a reputation for breaking their treaty obligations (though one major country doesn't seem to care at the moment), and there may be punitive repercussions for doing so, but it is about balancing the political effects of following the treaty with the effects of breaking it. If there is a grey area (such as some ambiguity about who attacked who) that often gives countries leeway for deciding whether or not to take action. It depends on the national and international political effects.

divibisan
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DJClayworth
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tl;dr: The side that wins the war is the one that was in the right.

In order to invoke the defense treaty, the attacking side will claim to be a defender, because they want the third party to be on their side, or at least to remain neutral.

Say the Philippines dress up a small group of operatives in Polish South Korean uniforms to attack a Philippine radio station. They then claim to have been attacked, and start continue the war in self defense.

Let's assume the US ends up joining the Philippines.

If they end up winning the war, they will make South Korea claim responsibility for the original attack on the radio station, and all is well.

If they lose the war, South Korea will make the Philippines claim responsibility for the attack and demand some kind of reparations from the US for breaking the treaty - the kind of reparations doesn't depend on the wording of the defense treaty as much as it does on the kind of relationship they want to have with the US going forward, and the sum of the military, economic, and political leverage they have. For example they might agree to drop any claims they have in return for the US changing sides mid-war, or they could sink the entire US Navy, invade the US, and instate a puppet government that agrees to pay monetary tribute to the Philippines for 50 years.

If there's a stalemate, everything has to be sorted out in one huge mess.

Peter
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  • This is the answer. A treaty is only as good as someone's ability to enforce it. The victor of the conflict will be the one to enforce it and exact penalties. If a country has conflicting treaty obligations, they will want to pick a side - the side that is going to win. – Seth R Nov 01 '19 at 16:27
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This question seems to assume that military support is a binary thing and/or that a mutual defense treaty typically has some concrete military responses spelled out, so that only another treaty casts doubt on the response. In reality, mutual defense treaties have ambiguous enough response clauses so there can be many more factors (besides another, conflicting treaty) contributing to variations in [non]response.

To pick a concrete example, NATO's putative response to a possible Russian aggression has often been discussed lately. The following tables from an extensive 2019 RAND report outline these issues: it finds that variation in response from NATO members could be significant, depending on a number of factors, including how they perceive the threat, their domestic political situation, and perceived consequences for [non-]participation:

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the gods from engineering
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