There was literally nobody else relevant in the game by that point but him and me. He wiped the Incas out completely, he took the capital of Sweden, Brazil somehow survived but...it's Brazil, you know.
If you liberate the other Civs, they won't be relevant in a "win" or "war" sense but they would have been relevant in a "world congress vote" sense.
It was a very specific situation and I'm more than happy to send you the turn 164 save if you think you can do better. Difficulty is 6-Emperor.
If you click "Go Advanced" in the reply at the bottom, if you scroll down you'll see an option to attach a file.