Well, i think that this post describes the problem in the best way.
You must give the player an option to follow history or not... there it is the fun of this game.

Also, like you said, the wars that are triggered by events should have very good trigger conditions, to avoid weird situations (well, that's almost imposible, but it should work in most of the cases

).
Also, some random factor is always great in this game, if not, the player "prepares" for the oncoming wars... something that the AI cannot do...

... In this case, you can always start the DESC: "Historically on...", so the player will know that this war was historically fought on that date, but in the game it could have been fought before or after that date...

.. that way, he will not be able to mobilize, prepare defenses, prepare the front, etc for the oncoming war.