A few months ago, I'd have said you could join SHIELD. Now it's SWORD, I think, but I don't know much about them. Those are more agents than soldiers, though. And then there's the police department, which is different from agents and soldiers.
There is an army, but it's for defending the country against other countries, not so much against the 'take over the world' types. At least, not my definition of those types of enemies.