I find it easier to design a game around a clearly defined story, whether this be from history or a work of fiction. History is so rich in interesting stories that there is no end to the games you could come up with.
Quotes about history
The spirit of my suggestion is that no historical events are off-limits, but good historical games are those designed to explore the contingency of history, which may be achieved by focusing on aspects of history that are no less interesting than the battles. I would like to think that it is possible to design good games that focus on the parts of history that we would rather forget, and by playing such games, come to a deeper appreciation of that history.