Michael Gerson assumes  that a hyperactive foreign policy is unavoidable for the U.S.:
Elements on the right and left apparently believe that reducing military resources will constrain future interventions. This is perhaps true of a European country. For America, with a set of unavoidable global interests, it doesn’t work this way. Constrained resources generally mean that interventions, when necessary, come at a later time, under less favorable conditions, from a weaker position [bold mine-DL].
In fact, I doubt that reduced resources will constrain future interventions. The decision to intervene in other countries’ conflicts and internal affairs is not necessarily prevented by a relative lack of resources. Prior to the hyperactive 1990s, the U.S. significantly reduced military spending at the end of the Cold War. That didn’t prevent numerous foreign interventions. There was not much meaningful political opposition to interventions in the ’90s. U.S. military spending is far higher than it was in real terms than at any time during the ’90s, so it would be wishful thinking to assume that minimal reductions in current excessive levels of spending would significantly curb foreign policy activism. What Gerson doesn’t address here is that the military interventions of the last twenty years have been almost entirely optional. The “unavoidable global interests” that supposedly compel U.S. intervention are not unavoidable at all, because in many cases U.S. interests have never been at stake in the first place. Military interventions in the post-Cold War period have rarely if ever been necessary, and there is no reason to expect future interventions to be any less optional than they are now. The question is whether Americans will listen to fear-mongering from the likes of Gerson or choose to ignore it instead.
If there are more constraints on military intervention now than there used to be, Gerson and like-minded ideologues have helped bring this about by agitating for one unnecessary war after another. The only constraints on future interventions that have any chance of enduring over time are political ones that are enforced by deep public skepticism about the desirability of new wars. The military budget should continue to be reduced because there is no justification for an annual base budget of more than $500 billion, but there should be no illusions that this is what will force the U.S. to mind its own business more often. The U.S. will intervene less often and for shorter periods of time so long as there are stronger political incentives to avoid new wars. If those incentives don’t exist, it almost doesn’t matter how large or small the military budget is.