Yale law professors Oona Hathaway and Scott Shapiro argue that it is in a New York Times op-ed:
If the United States begins an attack without Security Council authorization, it will flout the most fundamental international rule of all — the prohibition on the use of military force, for anything but self-defense, in the absence of Security Council approval. This rule may be even more important to the world’s security — and America’s — than the ban on the use of chemical weapons.
They are correct, of course, that evidence that Syria has used chemical weapons against its own citizens does not give the United States the legal right to engage in military action. I am a little less persuaded that bypassing the UN is as costly as they claim it is. Hathaway and Shapiro argue that the UN system deserves a lot of credit for preserving a norm that force is not a legitimate response to violations of legal rights:
For all its obvious failings, the United Nations system has made for a more peaceful world than the one that preceded it. No leader may claim the right to collect debts or gain thrones by going to war. States may fracture into smaller pieces, but they don’t get conquered. Gunboat diplomacy is also out of the question.
It is accurate that, as Martha Finnemore put it, the purpose of military interventions has changed over the course of history. It is much less clear how much of this is due to the UN system. Hathaway and Shapiro counter some of the obvious criticisms to that claim:
Others say it is legalistic, even naïve, to rely on the United Nations Charter, which has been breached countless times. What is one more, especially when the alternative is the slaughter of innocents? But all of these breaches add up — and each one makes it harder to hold others to the rules. If we follow Kosovo and Iraq with Syria, it will be difficult, if not impossible, to stop others from a similar use of force down the line.
You could add to this list of breaches any Soviet or U.S. intervention during the Cold War with the exception of the Korean war, which was authorized when the Soviet Union was temporarily absent from the Council in protest to the exclusion of the People’s Republic of China from the Security Council (Taiwan held the China seat at that time). As I have argued elsewhere (ungated, gated), the Security Council only started playing something that looked like its envisioned role after the relatively successful collaboration in the first Persian Gulf War. There is no evidence, for instance, that the U.S. even thought about seeking UN authorization for its intervention in Panama in 1989. The UN General Assembly voted that this intervention constituted a “flagrant violation of international law” but there is no indication that this mattered. President Ronald Reagan famously quipped about a similar UN vote on the U.S. intervention in Grenada that it “didn’t upset my breakfast at all.”
The point is not that it was right for the U.S. to circumvent the UN or to engage in the interventions that it did but that the UN cannot plausibly take credit for changing norms of intervention during the first 45 years of its existence. The UN was thoroughly dysfunctional in the area of conflict management. The end of the Cold War and the Gulf War experience made the UN more active. States saw domestic or international political benefits from asking for Security Council approval. Yet, there is no record of the UN actively restricting states from using force, let alone the United States. The U.S. either forged UN approval by threatening to go it alone or it went ahead without approval. It is not clear how avoiding the UN on Syria adds much information that should lead to substantial changes in beliefs about who will follow what rules.
I really wished there were a functional set of legal norms and institutions that could regulate the use of force. There are some norms that are obeyed and enforced quite well, such as the norm of territorial integrity. But the Charter system is dysfunctional as a legal system. Aside from the obvious problems with having five permanent veto powers that can block any collective action, the self-defense exception is prone to opportunism. Ever wonder, for instance, how the U.S. justifies its drone strikes in Pakistan, Yemen, and elsewhere? Well, we have declared a war on terror, which make these strikes acts of self-defense. One can agree or disagree with the validity of this argument but ultimately it matters little because there is no international legal institution with the jurisdiction to evaluate the merit of the claim (let alone enforce a negative finding).
The conventional wisdom is that UN authorizations are desirable but not imperative to U.S. foreign policy makers. This conclusion strikes me as correct. If you can get multilateral approval it is easier to get allies to support your actions and your domestic public may view an action as less costly and more likely to serve a good purpose. Multilateral interventions may also be more likely to succeed. It is worth compromising to get UN approval. In reality, however, the international legal system that regulates uses of force is not sufficiently functional to make UN approval imperative.
PS. Just to be clear: the point of this post is not to say that we should bomb Syria. It is an argument about the consequences of avoiding the UN if the U.S. decided to go this route.