Demand for American currency abroad brought stability to the currency. If that demand should diminish significantly, future American financial excesses will become a lot more dangerous. This might speed along decline or motivate a return to more disciplined economic policies. Time will tell.

The end of the ability to run deficits. Social Security and medicare financial problems become exponentially more urgent and dire.

no I'm talking about the part where poor Americans who join the armed forces go to foreign countries, are asked to kill people and sometimes die themselves

Especially Latin Americans.