I have a game where the entire world declared war on me because I as Napoleonic France didn't want to give up Louisville which I had fair and square colonized to America, Sevastopol which I had fair and square gotten in a peace treaty from Byzantium a turn after they had conquered it from Turkey or Russia to Russia, and Frankfurt which I had fair and square captured with the Grande Armée to Germany. In the very same turn every single civ was instantly willing to talk before I had even moved a unit. Most gave me all their money, some even offered a city, and only one or two actually demanded a little something from me in exchange for peace. That was the shortest world war I ever had, it didn't last even one turn and saw no combat action whatsoever. All it achieved was making me 1.000 Gold richer.
Two turns or so later China and vassals declared on me again for whatever reason, making China itself instantly collapse and the vassals give me yet more money before I had even moved a unit.
The funny thing is I wouldn't have gone to war over Sevastopol and Frankfurt (maybe Louisville though, I just finished the Winter or was it Summer Palace there) in the first place had the Congress taken place a few turns later, but it convened shortly before my second UHV would trigger and I didn't want to risk losing any land in Europe.
Actually I had a similar situation once as America with a Caribbean city shortly before 1930 that England demanded and the Congress granted.