It would be fun to see a game that covered the time between 1880 and 1905, when modern warfare really started in earnest.
Some interesting conflicts to look at during that time are:
-Spanish-American War (and the Filipino-American War)
-Russo-Japanese War
-First Sino-Japanese War
-First Italo-Ethiopian War
-Boxer Rebellion
-Second Boer War
I'm curious what some other people think, or what time periods others are in to.