I've been finding alliances quite stable too; I came back to my French VM campaign after being annoyed by Empire and its problems (not to mention the shooting is not nearly as gratifying as hitting someone with cutlery), and my alliances with the HRE and the Poles are going strong. I almost feel guilty for not helping the HRE out with the nasty Milanese, but the whole point was to get a secure flank so I could wipe out the English, Scots and Danes. Now I guess I'll have to go after the Spanish and Portuguese, but it's looking as if I'll have to betray my allies in order to achieve my goals. I was just so used to being backstabbed that I'm amazed at the permanence of the alliances--well over 80 turns so far, last I looked.

I'll be interested in trying out a campaign as the Turks after I finish this one.