The Westerlands just rebelled their way back into my game, and Balon Greyjoy is now King of both Iron Islands and the Westerlands.
http://imgur.com/a/wmQVA (http://imgur.com/a/wmQVA)
Joffrey somehow ended up being a Vale Vassal, so that might be the reason.
What does it say about Tywin? Does it say he left the realm or nowhere?
he's a vassal of King Balon Greyjoy if you look closer ;)