These are regions on the World Map that have one capital city for every Province. In order to make a Province part of your territory, you must be in a Faction and occupy the city. Only one Faction can control a Province. Controlling a Province will let you and your Faction gather resources from Elite Deposits within it. The more Provinces you control, the more bonuses you get. Your Faction can only attack a Province that is adjacent to its own territory. Provinces on islands can be attacked only if they have a link to other Provinces.

The amount of tiles a Province has as well as your Faction Rank determine how much Oil and Steel you will get in the beginning of the day. The more Provinces your Faction control and the higher your Rank, the better. :)