Players in Sid Meier's Civilization 6 will find themselves competing against many other civilizations in order to reach world conquest. However, despite them taking up territory and resources, players don't need to worry about competing against the various city-states peppered throughout the map. In fact, these city-states can be beneficial for players.
Throughout the game of Civilization 6, players will accumulate envoys that they can send to city-states. These envoys can bring different benefits back to their players depending on which city-state they were sent to.
The civilization that has the most envoys in a city-state as well as at least 3 envoys in the city-state becomes that city-state's Suzerain. This comes with many benefits that players will want to grab if they want an easier time when it comes to fulfilling their win condition.
There are multiple benefits that a player will get upon becoming that city-state's Suzerain. If players are tied in most envoys in a city-state there cannot be two Suzerains and there simply won't be a Suzerain until a player has more envoys.
The first benefit is that the Suzerain will be able to see up to three tiles away from the borders of the city-state. The Suzerain will also have access to the visibility provided by any units owned by the city-state. The Suzerain's units will also be able to heal at an accelerated rate while inside the city-states borders as well as have the ability to upgrade units.
The next benefit is that the city-state will be allied with the Suzerain player and will follow the player into war. If players are using the Gathering Storm DLC expansion, the city-state will additionally give +1 in Diplomatic Favor to the Suzerain.
In the case that a city-state is attacked, the Suzerain players will gain the Protectorate War Casus Belli against the attacker. If players are using the Gathering Storm DLC expansion, the Suzerain players will additionally gain Grievances against the attacking civilization. If the Suzerain player is at war, they may also pay gold to take control of the city-state's combat units for 30 turns.
A city-state's Suzerain will also automatically get imports of the city-state's resources. The Suzerain will additionally be able to build tile improvements for their own uses in city-state territory.
Finally, the most powerful benefit to becoming the Suzerain is the unique bonus provided by specific city-states. Each city-state has their own unique benefit that can be viewed on the envoy menu.
Civilization 6 is available now for PC, PS4, Switch, and Xbox One.
Source: Civilization Wiki