Because we act as a world police force?
Whether people agree with it or not, many countries in the world, even in the Middle East, have trade and alliance contracts with the U.S, that allows it to build armies to fight other peoples conflicts.
Germany is a prime example. The us can build bases there and station troops, and return, Germany can't build a large army or invest in armaments that would be considered too powerful. In the end, Germany profits the most by having a limited military budget.
It's just how it works. Also, the UN has an official statement that killing unarmed civilians is considered a war crime. The U.S uses it for the justification of Iraq, Afghanistan, and now ISIS. You just need a basic understanding of current politics.
I <3 Classic Platformers!
Multi-console Owner FTW
