I recieved a world domination message about the Turks in turn 148, summer 1154 (I am now in turn 169, summer 1165). I posted about it and someone said that you get that message when nother faction is close to getting 15 regions. If another faction gets the victory conditions first (World domination + defeating whatever factions), you can't win. He said you can still play, but you can't win. I don't know how true it is. I am still playing the same campaign and it hasn't told me that I lost yet. I'll let you know what happens when I beat France (it will be very soon).