I've been trying to play multiplayer with some friends, and generally been having fun until this inevitably pops up. An AI faction will demand a significant sum of gold as tribute. If you decline, this is treated as you declaring war on that faction, dragging your allies into a "Join Ally's War" screen. After they join the war, the game crashes. I get no "crash report" screen of any kind, no stutter or anything. It's like someone pressed Alt-F4 and closed the game.
It's made playing multiplayer with friends a constant fear that the AI will hold your game session for ransom. We can either pay whatever absurd amount of money the AI wants and severely damage our economies, or we can start a new game.