Civ is destroyed but another Civ still at war with them

[zoomer61]

I just killed off the last city of a Civ and yet another civilization after several turns is still at war this Civ. They don't exist, they have nothing.... I do not mark off the box that a civ cannot be killed off until every last creature is gone.

 

[Lord Yanaek]

Is it possible you and that other civ joined in a war against the "phantom" civ?

There is a possible bug that causes AIs to never make peace if they were part of a "joint war" unless their partner (possibly you) is eradicated.

http://forums.civfanatics.com/showthread.php?t=539353

 

[oldag07]

I have seen the same problem.