Paul Pillar discusses the illegality of an attack on Iran:

The charter of the United Nations is very clear in prohibiting the offensive use of military force, regardless of the nature of the underlying dispute. An armed attack conducted in the name of setting back a technical program that possibly could lead in the future to development of a weapon that other states, including the one doing the attacking, already have does not even come close to constituting self-defense as also mentioned in the U.N. charter. The international norm against offensive warfare, like certain other norms that also have become codified international law, reflects a broadly held moral standard. Not even the most inventive casuistry can justify, legally or morally, the launching of an offensive war to help maintain some other state’s regional nuclear weapons monopoly.

Pillar is absolutely right in all of this. Of course, the same could be said and has been said of NATO’s war against Yugoslavia and the U.S.-led invasion of Iraq. (Pillar mentions Iraq later in the post.) UNSCR 1441 did not authorize the Iraq war, and the U.N. passed no resolution on Kosovo for interventionists to misrepresent. The 1989 invasion of Panama was similarly illegal. Unfortunately, the U.S. and our allies have repeatedly violated the international norm against offensive warfare with impunity, and there does not appear to be much concern in the U.S. that this has undermined that norm. Like any norm, this norm is only as good as the ability of member states to enforce it, and when major powers choose to ignore this norm there doesn’t appear to be much that anyone can or will do about it.

There’s no question that the U.S. is harming its own interests by weakening the norm against offensive warfare. At some point, this could come back to haunt the U.S. at the expense of a U.S. client, but this doesn’t seem to be the way that many interventionists see it. As Western interventionists see it, there is one set of international rules for Western states and those aligned with them and another set of rules for others. Perversely, some of these interventionists imagine that they are shoring up a “rules-based international order” by waging wars that fly in the face of that very order.