how can we spend more on the military than the rest of the world put together and yet still need to hire mercenaries?
Because we're so paranoid about everyone else in the world that we
have to maintain an extremely large and expensive network of military bases around the world. Maybe if we weren't the world's police force, we'd actually be able to spend less on the DoD.
Out of the $685.1 billion defense budget:
$283.3 billion to "operations and maintenance"
$154.2 billion to "military personnel"
$140.1 billion to "procurement"
$79.1 billion to R&D
$23.9 billion to construction
$3.1 billion to family housing
So, we spend nearly a third of the budget just making sure our stuff still works and that it does what it's supposed to do.
We spend over $150 bill just making sure people get paid. Last I checked, the armed forces and the defense of your way of life was supposed to be a patriotic calling and your civic duty, not a profession. Alas, we have to make sure the people who want to make their living waging unnecessary wars under the brainwashed guise of "patriotism" and "national service" get their money.
Stupidly enough, we spend the absolute least making sure the families who deal with the hardships of spouses/parents being deployed have decent housing. A lot of it is outsourced now. Lots of cases of family housing being bug-infested and falling apart too.
Misplaced priorities much?