Near the beginning of the game, I took the green civ's first outpost. I had already made a first city, and, since I took his first outpost, he could not. He had a band of four hunting parties nearby, and I killed them. Several turns later, I made his outpost that I had taken into a city. At that time, I noticed he had another band of four hunting parties in the area, so I killed them. Much to my surprise, when I killed that group, another sprang up in the city I had made from his outpost. When I killed them, another band of four his hunting parties appeared in my city. At that point, I quit the game because this was obviously a bug. I don't know how many more times it would've happened or if it would have ever stopped.

Band of four tribes… do you mean one unit? Neolithic tribe players, who lose their last tribal unit are able to respawn—as long as they have not already went to the ancient era and established a city.

Changlini wrote:

Band of four tribes… do you mean one unit? Neolithic tribe players, who lose their last tribal unit are able to respawn—as long as they have not already went to the ancient era and established a city.

No, I mean four individual hunting parties stacked together into a single unit with four members. It was respawning directly on my city.  While it's good to know that I need to allow my neighboring AI get to the Ancient era before I exterminate them, this feels like a bug, and it would even if they hadn't selected my city tile on which to do their cheating re-spawn. 

Hands down, one of the most annoying things about the game in its current form is the "everyone gets a trophy" mentality. If someone gets taken out, they should stay taken out. History wasn't handing out trophies to the losing side in the Neolithic era. And, anyone who asks why I would want to exterminate the neighbor AI as soon as possible has only to look at the mindlessly aggressive warmongering and forward settling of the AI. Who wants that from a neighbor? Better to just get rid of them before they can start causing trouble.

I went back to this game after reading the above comment, and AIs who lose their last unit are able to respawn units as long as they've never had a city. I'm in the Early Modern era now, in part because I could kill the green hunting parties every few turns for the star. Somehow, the guy was able to get into the Ancient era, but he has no city because his hunting parties kept spawning in my city, and I kept killing them. So, instead of spawning four hunting parties, he's now spawning four scouts in my city. I have a couple more advanced military units sitting there, and they kill his units every time they spawn (earning promotions and stars). This is either a bug or a very poorly thought out mechanic. I've literally been advantaged by the refusal of this guy to just spawn somewhere else or die (which is what he should do). It's the early modern era, and this guy has been unsuccessful for 1000s of years. I mean, come on. He should not be in the running for a trophy of any kind. It's just silly.