The United States now spends almost as much on defense in real dollars as it ever has before -- even though it has no plausible rationale for using most of its impressive military forces. Why? Because without political incentives for restraint, policymakers have lost the ability to think clearly about defense policy. Washington's new mantra should be "Half a trillion dollars is more than enough."

After a decade-plus of war, the lessons for the United States are clear: fight fewer, more traditional wars and fight them more decisively. Above all, avoid getting entangled in the politics of chaotic countries.