.... and everyone is completely missing the point.
The fact to have a big army serve an economic purpose. Let me show you this :
http://en.wikipedia.org/wiki/World_energy_consumptionAn american use, in average, two times more energy than an European (EU-27).
In term of countries, only rich norther European countries use more, along with some petrol states.
It is true for other resources as well.
Now another thing. Why is European help so slow to reach Greece? Because as long as it linger, Germany can loan it money with very good interest rates. And why has Iraq been invaded? Because French companies has the exclusivity of it's oil.
US and Europe are allied, militarily, but are foes economically. Even among themselves, European countries fight for the world's resources. Not outright war, no, but in the third world dictators are pushed, aided and crushed by those fights.
The US army is not OP, it's too big, and too inefficient. The people who made your troops go into Iraq are stupid or corrupt (and most of them are corrupt).
It was going to be a disaster, and everyone warned against it. If anyone want a good laugh, read "The War Over Iraq". That idiot of William Kristol gloated that the debacle didn't happen,... right before it happened. Strife can say what he will, the war in Afghanistan and Iraq are two neat defeat for the US. Two defeat so costly it will cost you a whole generation.
And why? Because your army is completely inefficient, designed to fight in a conventional war who will not happen, and unable to fight the war of occupation who are asked for it.
And worse, even for the purpose of conventional war it's too costly. Having the best army in the world, well why not? But if you're not able to field it why bother?
Tl;dr : your army is necessary for your way of living and you need it. But it's too bloated right now therefore you waste money.