Peace Treaties are a feature introduced in the Bronze Age. They protect your base from attacks by other players for a period of time. As long as a Peace Treaty is active, your base won't come up when other players are looking for an opponent for a Multiplayer battle.
Peace Treaties are either purchased with Crowns or automatically awarded upon the defeat of your base by another player. In the latter case, the length of the awarded peace treaty depends on the extent of your base's destruction. A 12h Peace Treaty can also be gotten once a week from the Eiffel Tower.
Peace Treaties are canceled when you find an opponent for a Multiplayer battle or when you take revenge on a player who has attacked you, even if you end up not attacking your opponent. You will be prompted to confirm if you want to cancel your Peace Treaty.