Year 1502, turn 760.
It's been a while since I had played this far, so I was surprised and terrified when, after going on a conquering rampage against my neighbours, I went up to 30-odd cities (including a few offshore colonies) and noticed that I was losing around 1000
per turn due to all the maintenance costs!
Had to go down to 50%
for a while and focus on building up the newly conquered and resettled lands, and slowly but surely the economy went up.
Incidentally, that's why my Caravan numbers tend to be 3-digits.
All the warring finally gave me enough generals to settle in my military city to get enough xp to immediately promote new ships to Piracy (I was up to Frigates by this time), and that's how the seas suddenly became a much more dangerous place to be.
The AIs tend to go to war every once in a while, but they almost never get any results.
Prime example: Cochise (Apache) and Boudica (Celts). They share their own continent, are the worst enemy of each other, and regularly go to war, get a few generals each (meaning they both lose several units) and then sign peace for a while.
The border between them has not moved. Ever. It's in the same tiles it was when I had settled those Celtic cities several hundred turns ago when I was still using the Celts (this started as a High & Low game).
Revolutions I've seen happen to almost-dead civs (the ones being conquered by me at the time), they spawned a couple of civs holding onto the last couple of cities, which I left alone for awhile since they were in places I didn't need.
Later on I went and conquered them anyway, by that time they had been vassalized by someone I was at war with.
What did happen and was interesting was that both Boudica and me had several cities on the islands south of her (and Cochise's) mainland, and those requested independence, and we both granted those colonies their autonomy.
That also contributed a lot to reducing the insane city maintenance costs I was having.
Last note, Noble Knights, properly used and farmed, are insane killers.
As usual, the AI doesn't really know how to get the most out of them.