This is a 'thinking aloud' type of post, but that's one of the things blogs are for, isn't it?
Here's the question: What explains the apparent disjunction disconnect between global downward trends in armed conflict, on the one hand, and U.S. military and foreign policy, on the other?
It's fairly clear that the amount of armed conflict in the world, while not negligible, has been declining for a few decades (though the decline may have leveled off in the last several years). Joshua Goldstein judges that "[d]espite...complexities and some ups and downs, the year 2010 was probably the most peaceful, in terms of battle deaths relative to population, in the history of the world." (Winning the War on War, p.247) John Mueller and Christopher Fettweis, among others, argue that great-power war is either obsolete or on the verge of becoming so, an argument that has to be taken quite seriously in my opinion.
Yet the U.S. continues to act, in many respects, as if the world has not really become much more peaceful than it was in, say, 1950. Yes, the numbers of U.S. soldiers in Europe and Asia have been reduced somewhat in recent years, but the U.S. continues to have alliances or other security agreements with numerous countries, military bases all over the world, thousands of troops still in Europe and Asia (primarily Japan and Korea), and aircraft carrier groups able to be dispatched to anywhere in the world. Plus the U.S. still has some tactical nuclear weapons in Europe (I actually wasn't aware of this until seeing a journal article about it the other day) and also has invested in regional missile defense systems (or, in the case of the Persian Gulf states, sold Patriot missiles to them) ostensibly as protection from an Iranian missile threat which seems to have been overestimated. Moreover, the U.S. is executing what appears to be either an encirclement or a balancing (depending on one's view) maneuver against China, via the creation of a new or refurbished 'strategic partnership' with Australia, the selling of jets to Indonesia, etc. It is true that the Pentagon, faced with budget constraints, is planning to shrink the size of the Army and Marines somewhat and also, for example, is having to reconsider its plans for a major build-up on Guam, but this does not basically change the U.S.'s global military position.
So, given -- at least for the sake of argument -- that the world is more peaceful and less dangerous than it has been in a long time, why don't U.S. actions in the military/security arena seem to reflect this reality?
Some possible answers:
(1) U.S. policy is simply irrational.
(2) U.S. policy-makers don't think great-power war is obsolete and are generally stuck in an outmoded mindset.
(3) The U.S. global military posture is driven by domestic institutional forces, i.e., the power of the Pentagon and large arms manufacturers to influence Congress and the importance (or at least perceived importance) of the 'military-industrial complex' to the health of the U.S. economy.
(4) U.S. policy is a holdover from the Cold War. Elaboration: With the dissolution of the USSR and the resulting absence of a true peer competitor, the U.S. should have substantially cut back on its global military presence and commitments, according to both one strand of realist logic and 'ordinary' logic. This is what John Mearsheimer, to cite one prominent example, predicted. It didn't happen: there was some retrenchment but nothing like what might have been expected. (And NATO, far from declaring its mission accomplished and disbanding, expanded.) The reason was perhaps a combination of vested institutional interests, path dependence, and plain old inertia.
(5) Al-Qaeda done it. According to this view, had it not been for the 9/11 attacks and the subsequent decade-long reaction or overreaction (Afghanistan, Iraq, drones, etc.), the U.S. global military presence would be much smaller today than it is.
(6) U.S. global military dominance is supporting the U.S. global economic position (or what remains of it).
With the exception of #1 (which basically evades the question), I'm inclined to think there may be something to all of these answers, though I'm also a bit skeptical of #6. I would put the most weight on #3 and #4. But, as we say in the blogosphere, your mileage may vary.
Update: Another explanation for the puzzle might be that Americans are "an unusually warlike people," as Stephen Rosen argued in a 2009 article. I never got around to reading (as opposed to skimming) this, but the link will take you there if you're interested.