Two years later, the debacle in Somalia showed otherwise, fueling the timidity that followed in the face of the Rwandan genocide and the murderous disintegration of Yugoslavia. The Clinton administration did not stay out of the Balkan conflicts, of course, just as it did not quit enforcing no-fly zones over Iraq. But it limited the risks to U.S. forces, bombing from great heights and deploying peacekeepers only after the fighting had ceased.
That was the first post-Cold War cycle. The second, which began with the relatively cautious invasion of Afghanistan after 9/11, is now ending.
The exaggeration of our successes in Bosnia and Kosovo - both of which became dysfunctional international protectorates that only nation-building enthusiasts can regard as victories - dimmed memories of Vietnam and Somalia. Rapid initial progress in Afghanistan encouraged the hubris that led to the disastrous Iraq war, as well as a more extensive and ever more frustrating effort in Afghanistan.
But the flow of American blood and treasure required to prop up venal governments in those states eventually undercut enthusiasm for occupational warfare, especially amid an economic downturn.
Power gives American presidents more choices than other leaders. U.S. military capabilities and wealth make almost any global action possible. And the Cold War that checked much of our proclivity for intervention is over.
To fight as we do in Afghanistan, even most wealthy nations would have to hike taxes or slash other expenditures, provoking domestic opposition. We do it with less than 1 percent of gross domestic product, mostly borrowed.
Because we can intervene relatively cheaply, temptation always beckons. The world never lacks for civil unrest whose victims we might save. Congress' halls are rarely free of emissaries claiming we could advance liberty by fighting for the would-be nation they represent. And few years pass without outraged editorials arguing that American values and interests compel our troops to occupy some bloody corner of the Earth. Unhappy memories of recent wars are one of the few domestic forces that restrain us from those fights.
These contradictory impulses explain the incoherence of the U.S. war in Libya. The Obama administration naturally sympathized with rebels claiming to be democrats and overmatched by a particularly odious despot. But the two unpopular occupations already under way encouraged caution. The compromise is a limited air war meant to overthrow Moammar Gadhafi while minimizing the risk to U.S. service members and the cost to taxpayers.
The president ruled out ground forces before he articulated war aims. He resists arming the rebels, has handed over combat missions to our allies, and pretends we are enforcing a no-fly zone only to protect civilians - a fiction required to maintain the alliance. Rarely has a nation gone to such lengths to show its disinterest in winning a war it is fighting.
The allies' success defending rebel territory has not allowed the insurgents to fell the regime. If the stalemate lingers and costs mount, or anarchy engulfs post-Gadhafi Libya, the war will reinforce the caution brought about by Iraq and Afghanistan. But if things work out well enough for hawks to declare victory - if air power quickly allows the rebels to establish a revolutionary government - the resulting hubris will encourage more reckless campaigns.
Caution in American military policy is fleeting. We are so powerful and secure that even military debacles are insufficient to permanently teach us restraint. That is both a good thing and an endless source of trouble.
Harvey M. Sapolsky is a professor emeritus of public policy and organization at the Massachusetts Institute of Technology. Benjamin H. Friedman is a doctoral candidate at MIT and a research fellow at the Cato Institute. They can be reached at firstname.lastname@example.org and email@example.com.