City flipping... how and why does it happen?

I was playing a game of Civ1 recently, and three enemy cities rebelled and joined my civ over the course of the game! I didn't know this could happen in Civ1. Obviously it's not determined with relative culture point calculations like in Civ3, since there aren't culture points in this game, so what determines whether a city flips civs or not? Proximity is definitely not a factor; two of the cities that flipped to my side were deep in the other civs' territory, far from my borders.

I believe science is the major factor; the more developed, the more chance a city flips.

I think it's the overall development. I'm not completely sure but whenever it happened it usually happened that they admired a huge city with lots of improvements and wonders, while their own civ was relatively small. It did however happen to me once that I was building lots of wonders and keeping up in science with another civ. They already had armor rolling around and I didn't. So when a rather small city flipped to my civ it was immediately taken by their armor and I lost a tech.

Ah, I see. I was playing OCC - my first attempt at it so I was on Chieftain - and so naturally my one city was insanely developed and I had built all the big wonders in the game there, and I was also way ahead of the rest of the world on tech. I actually ended up winning the game with four cities even though I was playing OCC, since there's not a "We don't want it, rebuff the rebels" option like in Civ3 - you HAVE to take the city. I suppose I could have left them defenseless and started a war so they'd be recaptured, just to keep in the spirit of OCC, but I was already near the end of the game so I just let them be and kept building spaceship parts in my capital.

It's the precursor to Culture Flipping in Civ3! Actually, I've had that happen to me, and I think it's when you have fewer cities than everyone else, but have the highest population. Although, it's usually in the worst possible place. Once, Germany and Rome had respawned in South America (I had pushed them out of Europe), and a German city 'flipped' to me. Well, that was an automatic war with Rome...

City flipping is a dratted nuisance.

I get it a lot as I tend to play isolationist / perfectionist rather then world conquest. Infact Ive been known to send peacekeepers in to break up fights between enemy civs. I consider keeping all 7 civs alive to the end of the game a fun goal which can be quite hard at times. You just cant help some of them! (Yes Mao Im talking about you).

But, its really anoying to get extra cities you dont want. If Id wanted it Id have taken it already. ...

My opinion:

Unhappy Cities will flip faster than happy cities.