The Pentagon’s nearly unprecedented, wildly irrational spending binge.

This year, the United States will spend at least $700 billion on defense and security. Adjusting for inflation, that’s more than America has spent on defense in any year since World War II—more than during the Korean war, the Vietnam war, or the Reagan military buildup. Much of that enormous sum results from spending increases under presidents George W. Bush and Barack Obama. Since 2001, military and security expenditures have soared by 119 percent.

For most of that time, of course, the United States has been fighting two wars. Yet that’s not the cause of the defense-spending explosion. Even if the costs of the conflicts in Iraq and Afghanistan are subtracted, the defense budget has swelled by 68 percent since 2001. (All money figures in this article are stated in 2010 dollars.) The U.S. defense budget is now about the same as military spending in all other countries combined.

In a historically unusual twist, Defense Secretary Robert Gates, a Republican appointee and a former CIA director, has repeatedly acknowledged that military costs are untenable and decried the Pentagon’s “culture of endless money.” But despite Gates’s advocacy, and Obama’s backing, not much has changed. Congressional leaders nod in agreement at talk of reform—then demand that their pet projects be fully funded. A recent Gates proposal, received as if it heralded dramatic cuts, seeks merely to constrain Pentagon budget growth to 2 percent to 3 percent over inflation. At that pace, defense and security costs will hit a ruinous $1 trillion annually by 2030.

Pentagon profligacy is not a new phenomenon. But an ugly melee is brewing regarding America’s unsustainable government spending—and defense and security costs cannot be exempted from tough decisions over what the country can and cannot afford. And yet, security spending and military deployment are presented to the nation as virtually untouchable. If the Pentagon wants something, the logic goes, then it must be necessary. This is far from true.

The United States wields more military power relative to other nations than any country has ever known, including Rome at the peak of empire. The vast sums that America spends on defense buy many valuable things: a highly trained and ethical military; sophisticated and wide-ranging counterterrorism efforts; and extensive humanitarian operations, most recently in Haiti, Indonesia, and Pakistan. Furthermore, as Obama noted in a speech at West Point in 2009, the United States does not use its might to acquire territory or seize resources. Instead, the American military pursues what political leaders believe is best for the world. Such beliefs may be wrong, even tragically so. But has any other nation that possessed such overwhelming military force refrained from using it for conquest or pursuit of riches?