This is a great question. Here are Professor Caplan’s possible answers:
1. Libertarian commitment to non-interventionism was always much weaker
than it appeared. Rothbardians (and ex-Rothbardians who didn’t want to seem like
sell-outs) had key positions in the Libertarian Party, think tanks, etc., and
falsely claimed to speak for all libertarians. In fact, many libertarians held
the diametrically opposed Rand/Goldwater view that the U.S. should take off the
kid gloves and start “really” fighting the Soviets.
2. The movement away from natural rights and toward consequentialism
made libertarians more open to using government for good causes. Indeed, the
very fact that Islamic fundamentalism is a lot weaker than the USSR makes it a
more attractive target.
3. The movement away from philosophy and toward economics made
libertarians vulnerable to the simple-minded view that “getting tough” is a free lunch.
4. The rise of the “Establishment libertarian” led to moderation. In
the 70’s and 80’s, libertarianism was an alienated outsider movement. Over time,
however, many libertarian thinkers have been accepted into polite intellectual
society. The cost is that they had to distance themselves from “impolite”
5. The end of the Cold War revived the libertarian/conservative
alliance, making libertarians more receptive to conservative positions on
everything from foreign policy to immigration.
I think 3) is a bit of cheap shot, coming from a Libertarian who opposed the war – and one who loves to explain everything through biases. Historically, its reasonably easy to suggest that the true foreign policy bias (among English speaing peoples) is to ignore threats until they are extremely threatening. The book that I linked to mentions Prussian militarism, Nazism and Communism in addition to Islamic extremism. One could also add French Exapansionism under Louis XIV and French Nationalism during their Revolution to the list. Perhaps if we had “gotten tough” sooner we wouldn’t have been attacked, and hostilities never would have gotten as far along as they have (I haven’t heard anyone suggest that anything is free about acting in this manner). Nobody knows though – and that’s my main point.
I think 1) is the most plausible answer. I hope 2) is wrong (but I fear it is probably partly correct). I think 4) is a great point and operates on many levels. I wish Cato had stayed on the west coast. Everytime I see the weekly commentaries on the presidential elections on their blog, I cringe.
I wish 5) were correct but I think the opposite is true. I think one could ask not just about Libertarians, but also about Conseratives supporting the war. They went from believing nation building was bad and opposing Clinton’s tendency to intervene everywhere (all be it half-assedly) to supporting massive intervention and not just nation-building but complete state reconstruction. Similarly, Liberals went from believing that America should be helping people internationally and stopping genocide to promoting aggressive isolationism and arguing for maintaining the rule of a genocidal dictator. It seems like everyone’s foreign policy has gone 180 degrees in the last 7 years.