I mean we could make it like a World War 3 but with the different colonization of planets that some of these would hold some significant objectives like you said. Maybe one colony is a mining colony that exports the raw material for the titans and the ships and whatnot. Another may mine for precious metals or plutonium or some rare element that powers things. 

some faction is getting to greedy and decides to take over that colony or something and starts this massive international debate with another event that initially sparks a war.