Region
From AACWWiki
Region is the basic game space of AACW. A region can contains an infinity of units, of differing factions (coexistence is accepted). A region can hold several structures, which are gained or lost at the same time (either by combat, event or loyalty shift): City, harbor, depot and fort.
Regions have a military control value and a loyalty value, both tied to a faction (from 0 to 100). Others parameters are: nature of terrain, weather, in fog of war or not, playable or not (some regions can be unblocked by events).