Because the movie isn't about political happenings. It's about war. It's not supposed to be about "yeah this exact set of events would happen." If anything I'm glad they chose something outlandish.

Immediate edit: I'm trying to find better words to say it, but having trouble. Obviously war is political. I'm not saying the movie isn't political or not about specific political things happening today. I'm trying to say it's not meant to be about conservatives versus liberals and/or leftists or North versus South (like the actual American Civil War). But when I said it's not about political happenings it sort of came out wrong and I'm not sure how to say it succinctly.