Ross Douthat concludes a balanced post on Syria this way:

But as someone who’s generally sympathetic to anti-interventionist arguments but also believes strongly in the stabilizing power of the Pax Americana, I find this particular case a lot more difficult, and the president’s choices more defensible, than do many anti-war voices on the right and left.

There are a few things to add to this. To the extent that the “Pax Americana” has genuinely been a stabilizing force in the world since the end of the Cold War, it has been that way when the U.S. acts in concert with international institutions, and usually this has not taken the form of launching illegal military attacks against other states. The conceit that the U.S. can enforce international norms while blatantly violating international law seems clever, but it falls apart upon scrutiny. Even if the U.S. succeeds in reinforcing a particular norm through the use of force, it does so at the expenses of a commitment that is usually far more central to preserving international stability than the norm in question. When the norm becomes little more than a pretext for waging a war, obviously this undermines the norm at the same time. Thus the U.S. is reduced to making the claim that it is acting on behalf of “the world” when the vast majority of countries reject what it is doing. It is also not lost on Americans that maintaining “Pax Americana” has seemed to mean near-constant warfare for America.

The U.S. track record on promoting international stability in the last 15 years in particular is poor. As we saw in the case of Libya, even when the U.S. has international authorization its wars of choice can contribute to greater regional instability, and the decisions to attack Yugoslavia and Iraq in violation of international law had their own significant destabilizing effects as well. The expansion of U.S.-led security structures is often held up as an example of how the U.S. contributes to international stability, yet the efforts to expand NATO deeper into the former Soviet Union contributed to the tensions between Russia and Georgia that led to the August 2008 war. One of the problems with attributing “stabilizing power” to U.S. preeminence in the world is that the U.S. has repeatedly used its preeminent position in the last 15-25 years in ways that erode and in some cases directly attack international stability and peace. The fact that the maintenance of the “Pax Americana” has become frequently associated with waging unnecessary and sometimes extremely destructive wars makes its promise of preserving international stability seem hollow and self-serving. This is why it isn’t reassuring to opponents when this seems to be the best argument that one can make in defense of the proposed attack on Syria.