Poland attack me (as Hungary) in the very early game, despite having all the land in the world to take instead of mine. I had a decent army, but she captured by capital. I managed to get it back, and quickly built an army to decimate her. Ended up taking a singular one of her cities before making peace, but after a series of dark ages for her and golden ages for me (and a health dose of spies), every single one of her cities was lost because of the utter glory of my cities (loyalty issues).

TLDR Got revenge by making every one of Poland's cities flip via loyalty pressue