Well back in MTW, excommunication was a big thing. Here in MTW2, it isn't nearly as important. Most people can just shrug it off, and keep up their merry conquering.

So I'm thinking that maybe make the Pope more "proactive" in his excommunication threats when two catholic factions attack. Maybe even declerations of war should hurt papal rating. Excommunication should lead towards any catholic nations with a desire to start war declaring and joining a crusade against you.

Then, program the AI around desiring good papal relations. This way, the catholic factions only attack under extreme circumstances, and honor alliances as long as the player's papal rating is good.

What do you think? Maybe some factions, not all, could be programmed to be more responsive to the pope, such as in the above manner.