Quote Originally Posted by drone View Post
A reemergence has to have a "seed" province, a province previously owned by the dead faction that is under 100% happiness and triggers an uprising. I think that if any of the other provinces previously owned by the faction are under 120%, they get sucked into the reemergence. So as long as you keep your provinces over 120% happiness, you don't need to worry about losing a province to reemergences.
I think it's pretty clear from the manual, the game interface, and frogbeastegg's beginners guide, that rebellion only happens when happiness drops under 100%. It is recommended that you keep all your provinces at >= 120% because there are things that will drop the happiness in one turn so you want a bit of a cushion. Frogbeastegg says that the auto tax management in the original game aimed to keep happiness at >= 100% and that caused problems (for instance, when your monarch leaves the kingdom to a less competent son) when happiness dropped at times. With VI the auto tax management aims at 120% so that a small, quick drop keeps you over 100%.