Not really... the Cuban's filter up through Mexico. The teenagers are local guerrilla fighters. Happens all over the world.
Oh yeah, that's much more plausible . . . Sure, but only in places conquered and occupied by enemies. That has not happened to the US since 1776 and it is highly unlikely to ever happen again. There is simply no one with the capability to do this. Not even the Soviet Union at the height of the Cold War had any chance of actually invading and occupying the country. They could have fucked us up badly, but it would have been our rubble. The closest thing to an occupation we've ever experienced was when the north half of us invaded the south half. Even then, it was a stand-up war and not a guerilla war. Red Dawn was a fun movie, but it was preposterous, as many fun movies are.
