In Civilization 5, there are City-States scattered around the world. You can bully them for lunch money, ally with them, and declare war on them. If you conquer enough City-States, you'll eventually persuade them all to band together and declare permanent war on you.
If a City-State that declares permanent war on you is then captured by another civilization, and you liberate it, does it end the permanent war? Or do City-States never forgive and never forget?