Loyalty is a feature added in the upcoming Civilization VI: Rise and Fall expansion pack. Here's the lead designer Anton Strenger on the subject: The stakes of the new Loyalty system are huge because, at the extremes, it can flip control of entire cities to different players without military force. Low Loyalty in a city puts it at risk of rebelling and becoming a Free City. That, in turn, makes it a juicy target for other players looking to expand their own empire. Keeping your cities loyal not only keeps it on your side, but also emanates its Loyalty as a kind of “peer pressure” to other cities nearby. You could even sway cities from other civilizations to join you.