How to avoid excommunication?

[Dragoncrusader]

To avoid excommunication, you have to withdraw from the territory and send a diplomat to arrange a ceasefire - otherwise you are still at war. If you do not get that ceasefire you will get excommunicated.
But here is a clever ploy, declare war on one faction and then on another immediately, followed by a ceasefire on the first faction. The computer can only keep track of one excommunication at a time and so does not recognise the second war and you can obliterate the faction at your leisure. I would not recommend fighting the Pope. His faction always reappears with massive armies and you end up having to garrison central Italy with a large army just to keep him under control. Why not use the Pope instead. Strip a province of defences, wait for your neighbour to invade and then crush him when he is excommunicated.

[Procrustes]

Actually, he gives you two years to stop your agression, so you have one more turn to assault any castles in the provinces you just took - then you can keep them as long as you don't attack the other faction for ten years. You can remain at war with them during that time, but you can't attack them. At the end of ten years they are likely to attack you if they have any fight left in them - if you are patient you can chew up whole empires by taking a bite every decade or so - have done this to Spain and HRE many times.

Sometimes they will attack you and get excommed themselves - then you can get medeval on their ass.

Note that when the pope dies all excommunications are void. So if you really want, wait until he is old and you will only be excommed for a short time. Or have a couple good assassins ready....