This is far from conclusive, but in the latest game I'm playing, the price of peace has gone UP when I've destroyed a vassals units. Before killing a caravel, 395, after killing his vassal's caravel, 410? In another case in the same game, I wiped his vassal's stack, and while I lost some units, I clearly came out way ahead, and the price of peace went from 690 gold to one of my weak cities. Later, after taking one of his vassal's cities, it went from my weak city to a core city! (this last one is kind of neutral though, as I seem to recall war success of taking cities is actually quite low, and I lost more units than they did). What gives? Is this a known bug?