Has the papal states ever expanded on your game?

Pretty early in my HRE campaign, I have taken Florence and now the Pope (or one of his Generals rather) is sitting just outside it with a full stack of pretty good units. He is just standing there, doing nothing for the last 10 or so turns.

I have put some more defenders in the city but nothing is happening.

When I pulled some forces away, thinking he wouldn't attack anyways, he moved that stack to Bologne and is now looming over that =S

My standing with the Pope is fairly low because I just defeated Venice and executed their faction leader after capturing him in battle, so I guess, I will leave some more units down there.

The damnable pope just attacked me in my game. No real reason, but the low standing with him might have to do with the fact that every catholic nation close to me seems to want war, which somehow makes the pope hate me for fighting back. well I'll show this guy what's comin to him.

weird in my game the pope always captures Valencia in eastern Spain.

In the campaign I'm playing as right now (Egypt) the Papal States went at war with Milan and now owns Rome, Florence, Milan, and Genoa. Most campaigns they usually just have Rome, or Rome and Florence.

It is possible. In my game they landed the full stack which is usually protecting Rome to Eastern Spain, to my unprotected flank. Quite a nasty surprise. I have also seen S.P.Q.R expand in RTW, when they bribed one of my cities.

It has to be with his traits. Warmonger or pacifist. Get a pope that is a warmonger early on and possibilities will be that he will have an empire.

He will attack you if you are encroaching in his lands, you're not allies, no military access, and you have a mixed, dubious, or despicable reputation.