It's the military-industrial complex

Overspent and Overextended
Why is Washington spending so much on the military?

America spends more dollars on the military today than in 1986 or at any other point since World War II. The numbers are striking. Using 2000 for constant dollars, the U.S. devoted $774.6 billion to the military in 1945, the last year of World War II. In 1953, the last year of the Korean War, military outlays ran $416.1 billion. Peak expenditures during the Vietnam War hit $421.3 billion in 1968.

In contrast, in 2010, before the Afghan surge and other unplanned expenditures, the administration expected to spend $517.8 billion ($700 billion including Afghanistan and Iraq). That is more than during two large, hot wars. More than during a lengthy, often warm Cold War. And two-thirds as much as during the worst conflict in human history.