Do we know why the last war started?

The Prefecture of Ryu are set up as the good guys, yet the Takashi ousted the last ruling clan in a rebellion that hasn't really been given a reason. The Shiho don't seem as obviously evil as the other factions directly opposed to the prefecture, so what made the Takashi rebel?

I've considered using this setting for an rpg considering I have these nice painted minis, but I that seems like a very important detail to omit.