Source: http://opiniojuris.org/2012/09/12/u-s-ambassador-to-libya-is-killed-what-responses-are-legal/
Timestamp: 2019-04-24 02:14:30+00:00

Document:
U.S. Ambassador to Libya is Killed; What Responses are Legal?
12 Sep U.S. Ambassador to Libya is Killed; What Responses are Legal?
[I posted this originally at the same time as Duncan, so it is a bit repetitive, but I’ll leave its content basically as is].
Sad and startling news: U.S. Ambassador to Libya Christopher Stevens was killed yesterday in a rocket attack on the U.S. Consulate in Benghazi. This is an addition to another violent attack on the U.S. Embassy in Cairo.
the head of the mission.
prevent any attack on his person, freedom or dignity.
Plainly, both Egypt and Libya have massively failed to live up to their duties on these and other relevant provisions. The question is: what legal responses could the U.S. take?
Under U.S. constitutional law, the President has long been understood to possess the authority to respond to attacks on U.S. citizens and government missions with the use of military force. He can do this without first seeking the consent of Congress. See Durand v. Hollins, 8 F. Cas. 111 (CCSDNY 1860). In that case, a bottle was thrown at a U.S. diplomat in Nicaragua, and the court endorsed the legality of a “calculated retaliation after the fact” arguing that the nature of the response to such an attack rested with the discretion of the President. (The U.S. Navy bombarded the town in retaliation).
Of course, the legality under international law today of such a “calculated retaliation” is less clear. Indeed, my guess is that the typical response would be for the U.S. to demand punishment of the perpetrators, reparations to the U.S. and perhaps to the families of those injured, and an assurance of non-repetition. Failing such a response by Libya and/or Egypt, the U.S. could in theory try to bring the parties to the ICJ (but that didn’t accomplish a whole lot back in 1979 against Iran). And of course it could threaten to retaliate against the Egyptian and Libyan governments. It seems the best case for military force would be if the U.S. believed it was necessary to protect the safety of U.S. citizens and diplomats.
I doubt that there are any plans to use military force here, but I do think it is worth considering whether and how such a response would be appropriate and legal.
I’m not sure we have any recourse we really wish to pursue, since the Libyan government doesn’t seem to have intentionally committed the offense.
Jordan is no doubt correct about what will actually happen.
That’s the kind of statement you really need to substantiate. As Duncan explained, the obligation is not one of result – the fact that Amb Stevens was killed does not automatically mean that Libya has breached its obligations. Libya would be responsible if it were either involved in some way with the carrying out of the attack, or if it failed to ‘take all appropriate steps’ to prevent the attack.
Also, the legality under international law of any ‘calculated retaliation’ is far from unclear. UN Charter Art 2(3) and 2(4) are very clear, and an argument based on self-defence is a very long bow to draw in this case, particularly if Libya were not involved in the attack.
From a practical perspective I’m not sure what utility a military response would serve, beyond satisfying our primitive and visceral desire for revenge. More generally, why is it that the military option is the first to spring to mind to solve seemingly any problem?
Actually, it would be self-defense against some non-state actor(s), not against a state, and quite permssible if they have been involved in prior attacks or ongoing attacks. Also, U.N. art. 2(4) raises questions re: interpretation: (1) one view, unsubstantiated by the text as such) is that all uses of armed force against a state are impermissible, and (2) another view is that the article only expressly prohibits three types of force, two types against a state and a third category. Using the latter approach to interpretation, it may be that some U.S. use of force is not against a state as such and would in any event not be “against” the “territorial integrity” or the “political independence” of some state and, on balance, would be generally serving of the various purposes of the Charter identifiable, for example, in Articles 1 and 55 of the Charter (with or without the consent of the state of Libya, for example, and whether or not self-defense is permissible under Article 51).
‘Query “almost universally”‘. Unfortunately my local law library is now closed, so I’ll have to park this one for the moment. (Please don’t judge me for considering hitting up the law library on a Friday night).
On your second point, I’d suggest that the overriding ‘object and purpose’ of Art 2(4) is to set some very strict limits on the use of force, and that accordingly it should be strictly interpreted in pursuit of that object. The principles underlying the prohibition have been elaborated on in subsequent resolutions and practice of the Security Council and General Assembly, most notably the Friendly Relations Declaration and the Declaration on the Inadmissibility of Intervention in the Domestic Affairs of States.
Thanks also to Opinio Juris and Julian, and to Jordan for prompting me to reconsider my position on some of these points.
That’s a good shift to object and purpose of 2(4), which begs the very question at stake, since the real focus of art. 31 of the Vienna Conv. on the Law of Treaties is on the object and purpose of the treaty (thus, all those others in the Charter that are specifically identified as such in art. 1 and otherwise elsewhere).
Art 1 aspires to an international order in which disputes are settled by peaceful means, in which such forceful measures as are necessary are taken collectively, and in which international cooperation and friendly relations are accorded due respect. Expanding the narrow exceptions to Art 2(4) does not (in my view, at least) serve these aims.
In any case, one must also (per VCLT Art 31(3)), in considering the context of a term, have reference to any subsequent practice or agreement as to the interpretation or application of the provision. That provides ample justification for considering the resolutions I mentioned above, among other sources.

References: v. 
 Art 2
 art. 2
 Art 2
 art. 31
 art. 1

Art 1
 Art 2
 Art 31