I'd say a world after a Great War would be an awesome thing to play with, but not after things have subsided, that would completely defeat the purpose. I mean imagine a world just recovering from such a thing, with the craters from the bombs still in the ground, the trenches still dug, the people still in poverty and relying on a government to make it all better again. A government that might not have the well-being of the people in their interests. Now that is a setting you could really play with.
In fact if I hand't just started a new rp that would've been a setting I could dive nose-first into. Especially playing with the scars of the people and the distrust for foreigners that would be triggered, it would make for a pretty dark roleplay.
But maybe I've just been reading too many war books.