I've noticed that, starting on Noble I guess, the AI capitulates cities very quickly. They start a war with some other civ and, instead of just ending the war, it ALWAYS makes it his vassal. Since I've yet to familiarize myself with this thing, I'm constantly having to defend myself from a civ that has sometimes 3 other civ's as it's vassal...which makes it nearly impossible for me to win. So I wanted to understand how it works. I tried to make a civ my vassal sometimes but they always say that they're doing fine on their own. What scenario is necessary for this to happen? I couldn't find a good article regarding this subject.