There's been enough discussion about the event in the Tea House to make me think it deserves its own topic in this forum. Mainly, I want to figure out exactly what gets the game to decide that it's time to throw everything it has at you. As I myself have only encountered the event once so far, I won't be of that much help providing anecdotal evidence, so this initial post will be more of a "general factors/questions" thread.

What we know: Realm Divide is caused by your clan's reputation bar to be full. This event happens immediately after that condition is met, with the actual war-declaring to take place the following turn.

What we're not sure of: What exactly gets the bar to move all the way up? Does the province limit differ depending on chosen faction, game difficulty, and campaign length? Is there anything tied to it aside from the capture of cities (for example: Daimyo stats or a lot of notable victories)?