I’d say that the fall of the Soviet Union discredited several ideas on the left and the right: on the left, the idea that the state should own most of the means of production; on the right, the idea of isolationism, or non-interventionism. It is now patently obvious that if the US had not drawn a proverbial line in the sand through Germany, the Soviets would now own large blocks of Western Europe that would be struggling in the same way that Eastern Europe now does. ~Megan McArdle, responding to Bryan Caplan

Yet it is the fall of the Soviet Union on account of its own internal weaknesses that suggests just how unnecessary interventionist policies really are from the perspective of the American interest.  Had it been taken over by the USSR after the war, western Europe would have been more, not less, indigestible than eastern Europe and might well have hastened the break-up of the Soviet empire.  One might say that it is “patently obvious” that had the United States not entered WWI, at least one of the great totalitarian nightmares of modern history would probably have never come to pass.  Looked at this way, U.S. interventionism hasn’t really been a credible foreign policy since its inception, and the upheavals of the end of WWI and the interwar period ought to have made it disappear forever.  However, even if it were the case that the Cold War was exceptional and required a different response, the Cold War ended twelve years before the invasion of Iraq.  It isn’t as if the ’90s offered overwhelming proof of the efficacy and wisdom of intervention.  Furthermore, our experience in the Cold War argued for continued containment of Iraq rather than an adaptation of the irresponsible doctrine of rollback.  In short, there is almost nothing about the Cold War or post-Cold War experience that explains why some libertarians supported an aggressive  invasion of a Near Eastern country ruled by third-rate dictatorship.  If libertarians were wrong to be non-interventionist in the ’70s and ’80s (I don’t think they were, but let’s just suppose), it is remarkable how a good number of them could then turn out to be wrong by becoming supporters of intervention in Iraq.