I think a WW2 setting is a no brainer (eventually), but there is a lot of history between the revolutionary war and WW2 which could be filled in first, such as the civil war as you pointed out.
After WW2 there is the Cold War which would make perfect sense, and beyond that there is the current war on terrorism which would sorta see the series going full circle because that would bring it right back to the middle east from where it began.
They could even take it into the future and have the event take place on another planet. That could make it very similar to the Red Faction games.