Okay, here is a small history what i did to have it:
-Attacked Rome while papal states was my ally,
-Captured it and cornered the last papal army,
-Killed about 9 popes one after another until my poor cardinal is the only one left:),
-İn the end i have the pope seat, but...

Naturally, my actions caused all catholic factions to declare war on me and soon
(i couldnt killed one pope for 3 turns, so he had the time to call a crusade) they
all sent crusading armies to Rome.(yes all catholic factions, it was funny to see
6 crusading armies passing by Venice together:))

But now i have the pope, he reconciled me, ended the crusade, loved me:) but will he tell them to stop attacking me and if they siege one of my cities will he excommunicate them?İts not good to have 6 full strenght armies around my capital because i cant clean em up sooner or later,im out of men...

(i tried to offer ceasefire but even if i give 100000 florins, they find it very demanding for ceasefire..)