Everyone in the city has worked hard for you, so you should reward them for their dedication and loyalty. This is important as happy workers will stay loyal, while unhappy people will soon leave to look for a new home.
In the City interface first click on the palace. Then, click City info to view information about your city. Click Pacify, found next to the loyalty cell. Finally, click Relief and click OK. Once you have pacified your people, no further operations of this kind can take place for 15 minutes.