OTL: Frederick II, King of Sicily, King of Cyprus and Jerusalem, King of the Romans, King of Germany and Emperor of the Romans, waged a war against Pope Gergory and the Guelf factions of Italy in the name of the temporal power of the Emperor. However, in 1241 just before Frederick was to attack Rome itself after a successful campaign, Gregory died and Frederick ceased his invasion.
What would have happened had either Frederick continued his invasion or the Pope not have died? What effects does the extinguishing of the Papal States have on italian unification, the renaissance, etc.?