Here's a challenge for you - find a way to make it so that, after the end of a WWII analog, the two major powers in the World are Russia (Tsarist, Communist, whatever) and the British Empire/Commonwealth, and that they promptly get into a Cold War. The British Empire has to have broadly the same boundaries as in OTL - you can't just decide they shall conquer China or anything. As a suggestion, it seems likely that Britain will try and contain Russias southern expansion using India as a base, and that they would have Japan and the Ottomans (if they still exist) as allies to prevent Russian expansion in other directions.
In addition, the US can't be a superpower (obviously). It can be a great power, but either so isolationist it doesn't really care or weakened to some extent.
Disclaimer: I wasn't sure whether to put this thread in the pre-1900 or post-1900 board, because it kinda straddles the period, but if it should be moved, move it.