I have a game going on Civ5 kinda like this, but not just really far into the future.
I turned all victories off and have just been trying to run a peaceful country.
On a continent with about three other Civs, I built up a pretty good country and eventually had about three city states that were just about perpetually my allies.One of them I liberated from the Ottomans.
Once France, who was on land that was connected to my continent, declared war on me.I responded by taking all the cities they had to the north of me on my continent and then making peace.I think I may have tried to liberate a CS that was on their continent during that war, but I couldn't really liberate it because it still had units left, and, thus, was not completely out of the game.So I just held on to their city.
Eventually, France, along with Russia, declared war on me again and France took back the city state that I had captured from them.This time, however, I decided not to go so easily on them.France had cities across a narrow channel of water from my continent to theirs.I took two cities right across the channel from them and then proceeded to help the Songhai, who were also at war with France.France had been taking a good many of their cities.So my invasion fleet set off and landed on that continent and began beating the French back, and restoring Songhai cities to their control.I also liberated another CS from France that had originally been captured by someone else, but France had captured it.
And during that big war with France China had also declared war on me, even though they were on another continent.But I had a city on their continent pretty close to them(Sound like that could have been the reason they attacked?).They proceeded to attack my city on their continent, but never did take it, and I eventually made peace with them.I also eventually made peace with Russia, and I think they eventually joined me and the Songhai against France.
Since France would not agree to give me back the city state so I could liberate it, I eventually fought all the way back to that city state, took it, and liberated it, and that was the end of that war.
But shortly before the war with France had ended, the Chinese declared war yet again and once again started attacking my city on their continent.Although I had not used any nuclear weapons in this game, the Chinese dropped two Atomic Bombs on my city on their continent.So I decided to take some more troops over to their continent, along with some of my own nuclear arsenal.But the city they were attacking was my only source of uranium, and I think one of the Atom Bombs destroyed the mine, so I was lacking uranium.So I started looking for a city state to buy up to get it back.I eventually found one that had enough, and got it as an ally.
So I'm still at war with them and my forces are heading that way, and that's as far as I got.
It's been a fun game though.