Sweep of history games, such as Britannia and its spinoffs, History of the World, and others (Eurasia and Rise and Fall of Assyria are two of my prototypes), are never far from my mind. I have two all-of-Europe games as well, and have dabbled with several all-of-China games. (China's current boundaries, and Europe, are close to the same size.)
A problem in an all-of-Europe sweep of history game is keeping the small nations extant. Historically, small nations tend to hang around in Europe, complete with separate languages and sometimes separate cultures. The problem in a Chinese sweep of history game is that the dynasties dominated (at times), so getting rid of the chafe is necessary. The small nations can't be allowed to stick around TOO long.