Without Security Council authorization, any U.S. military force to respond to Assad’s chemical weapons attack would be a violation of international law, but …
Policymakers would be well advised to know the relatively long list of cases in which states have engaged in humanitarian intervention without Security Council approval, and not paid the same political costs that would come with predatory uses of force.
Here’s what I wrote in October 2013:
Illegal but not unprecedented
If the United States does use force in Syria without a Security Council go-ahead, its actions will be illegal—but not unprecedented. There are several more cases than Kosovo. In the earlier phase of the UN Charter, Tanzania invaded Uganda to oust Idi Amin, India launched an invasion in response to massacres of civilians in East Pakistan, Vietnam invaded Cambodia to oust the Khmer Rouge, and India flew military jets into Sri Lanka to escort cargo planes dropping supplies to Tamil civilians under attack from the Sri Lankan forces. These were, of course, also mixed-motives interventions, but the humanitarian element reduced the international opposition to them.
After the Cold War, such interventions without Security Council authorization were conducted by multilateral coalitions. The US, France, and the UK conducted years of safe havens inside and No Fly Zones over Iraq initially to protect the Kurds and later to protect the Shiite population as well. Other states assisted by providing for bases and flight paths. The US, France, and the UK invoked Security Council Resolution 688 to support their actions—but any close observer knew that was a legal hoax. Indeed, the Resolution was purposefully not issued under Chapter VII of the UN Charter, because Russia and China promised to veto any such reference. In a leading book on the contemporary history of humanitarian intervention, Nicholas Wheeler explained (in a lesson that the White House today could have benefited from):
“How, then are we to account for the fact that no Security Council member who voted for this resolution publicly challenged the West’s legal right to create the safe havens?… ‘Chinese and others … were willing to tolerate actions de facto that they would not authorize de jure.’ (quoting Jane Stromseth)…
[N]one of these states wanted to be exposed publicly as opposing a rescue mission that was saving lives and they were shamed into silence. Acquiescence, then, rather than tacit legitimation captures the response of those governments to Western intervention.”
In the early 1990s, the Economic Community of West African States invaded Liberia without prior Security Council authorization. And, the coalition later invaded Sierra Leone without getting approval beforehand. Most recently, NATO’s actions to oust Qaddafi arguably exceeded the authority granted to it by the Security Council.
The U.N. Charter not only prohibits the use of military force but also the “threat” to use military force. I am sure we could find even more cases in history where States have threatened to use unilateral force for humanitarian purposes. One of the most recent precedents, of course, is President Barack Obama’s declaring his intent to use force in response to Assad’s use of chemical weapons as long as Congress–though not the UN Security Council–would support his actions.