who fights in he American army?
All sorts of people. From South Americans, who want an American citizenship over ghetto people, who think an army service will give them opportunities, to people like the sons of John McCain and Sarah Palin, who do it out of conviction, that fighting for their country is a great thing.

Why are they there?
For different reasons, as already pointed out. Oppotunities and nationalism both play a role.

What would they be doing otherwise?
I don't know. But it is irrelevant for the question if they do a great honourable question for their country. If they are slaves, it would be the most important thing to liberate them, not to laudate them for what they are doing.

Der Amerikaner ist die Orchidee unter den Menschen
Volker Pispers