Re: Kill the pope!
I've killed the pope more than five times in my campaign when he began to favor several countries at my total expense.
For example, I was about to wipe Milan off the map at the same time when the Pope demanded that I stop fighting. Deliberately! I agreed until the orders were up. After I had conquered Milan, and was about to wipe the last Sicilian city off the map, the same Pope ordered me to stop. After I agreed to this orders, I destroyed Sicily, and then assassinated the Pope.
The new pope had nothing against me, and nobody knew I had done it.
Now, whenever it looks like the Pope will turn against me, I assasinate him. I've already done this at least five times, like I said.
Remember, it's not murder if he joins the enemy (in a manner of speaking) to ruin your country and plots against you!