American civil war and independence seem great topics for a game but i dont think its big enough for a and a.
Rome and Napoleon seem the best choices. I think Napoleon wold be the best suited for axis style games. But I’ve been searching for a good Rome game since I can remember. Wish there was one with the system like Napoleon in Europe, or something.
My own ideas would be:
Age of Imperialism
The scramble for Africa, establising seapower, forming Germany and Italy, etc.
Age of Sail
Establish colonies in the New World, securing vital trade goods and fighting natives.
Thirty Years War
Interesting battles and politics in Europe.