Oh man, this is too funny! I was just gonna post about this myself!
I am playing on Prince and trying to learn how to play on that level (I don't normally play past Chieftan) and decided that I wanted a Domination victory before the game started. So, I am playing as Germany. Fairly early on, I wipe out Siam and it's three cities by accident (Fog covered the fact that Siam's capital was their last) so that hurt me in diplomatic relations with my other neighbors, that at this time, I hadn't met yet.
So, getting to the reason for my post. It's centuries later and my civ has grown like a tower up the middle of the continent it's on. To the northeast is a rather expansed China, to the northwest is a mouthy Japan, and to the west is a clueless England. I finally have enough of Nobunaga and get mideval on his heinie. He sues for peace and offers me 3 cities as part of the deal. I accept because my military is getting strung out and Wu is getting pretty bold herself in her statements. We all know how much German's love 2-sided wars
So, It's a few turns after the peace treaty has expired and Oda decides "Hey! I have a couple of Samurai. Let's squash Germany!"
So they immediately re-take one of the cities they gave me in a peace treaty because it was on the far side of the Japanese empire from me and I couldn't garrison it and came after me. A few turns after this, Elisabeth decides that now is a good time to attack since I'm distracted with Japan. Now I'll be honest. The British force that came after me was much bigger than I had anticipated. Anywho, A few turns after this, Wu Zetian comes after me because I have land and precious resources that she needs and won't risk losing them to another civ.
So at this point, I think I'm screwed. But I battle on, playing a purely defensive game and eventually push back all 3 attackers. All 3 treaties offer me cities which I graciously accept, expecially since some of those cities were very strategically placed and I was appreciative of not having to actually fight to get them.
Now for the fun part. I puppet them all and find myself at -106 happy at the end of that turn! I had rebels pop up that I didn't even know existed! I've never had enough unhappy to get rebels before.
But the other thing I noticed was that I was getting 6 unhappy per city instead of the usual 3. This applied to cities I puppeted via peace talks and cities I took forcibly. Why did this happen? It's around turn 300-350, I think I'm in the renaisance era (possibly the industrial, I think I have access to Coal), playing on Prince difficulty as Germany.