There is a maximum change per turn limit, you know. It's set in the happiness.txt file and I think it's 20 percent for all types. If they had been rioting for a long time they might be well over 100 percent 'unhappiness' and it would take several turns to neutralize this. I'm not sure how high it can go, or now it decides that rioting has progressed far enough to cause a full rebellion.
BTW, one way to make the 'bloodthirsty' happines type useable is to make troops more effective at increasing happiness. Rationale would be that troops inspire 'patriotic' feelings.
Then, the happiness hit from treaties other than war can be controlled by having at least a few troops on all your planets.
[This message has been edited by Baron Munchausen (edited 09 September 2001).]