I ended up running a military campaign across the entire world because nobody would stop being hostile, then I eventually lost as my own cities rose against me.

It was my first Civ campaign, I played it in one go for hours upon hours until late at night.

The feeling of utter futility after complete domination is still memorable to me, it was such a strange feeling.

Just for information, how endgame is an endgame in Civilization? I assume at some point you do so well that you can’t do anything else and all new nations must bow to ur immense nuclear power

You must not have enough nukes.