Editing Civilization IV (section)

===Units and combat===
[[File:Civilization IV Print Screen.png|thumb|upright|Example of some of the units and 3D graphics unique to ''Civilization IV'']]
Most units that the player can generate and use are military units, with certain attributes such as combat strength and movement rate particular to each military type. Each unit can gain [[experience point|experience]] through combat, which later translates into promotions that the player can use to assign military units new bonuses.<ref name="ignreview"/> Initially, most combat takes place on land, but further advancements in the game's [[technology tree]] can allow the player to build ships and planes with which to fight battles on sea and in the air. Any number of units can be stacked onto a single space and move as a group if so assigned, but the overall combat phase is resolved by one-on-one unit battles.

Combat is initiated when moving military units are moved onto the square occupied by an opposing force's military units and cities, and combat is then resolved with calculating statistics of each unit combined with some [[random number generation|random chance]].  Defeated units are removed from the game (apart from workers and settlers, which are captured by the attacking force), and any attacking units that are able to defeat the last defending military unit on a space will move to occupy that space.  If the space is occupied by a city the player may choose to occupy and capture the city as their own or [[Demolition|raze]] it. Other than combat, military units can also be assigned to fortify a specific space, perform sentry duties, destroy enemy city improvements, or explore the game world.

Non-military units include settlers who are used to found cities, workers who are used to improve space and gather resources, spies who can perform [[counterintelligence]] and [[espionage]], and religious missionaries who can be sent to convert different civilizations and cities. Also, with the Beyond the Sword expansion, new units are added such as executives, who can spread corporations to new cities. Throughout the game, players may also generate a special unit called a "Great Person". These are named after historical figures and can be used for one-time advantage boosts in various ways; examples include Great Engineers who increase overall production levels and Great Scientists who improve technology. Assigning inhabitants of cities to work as 'specialists' (scientists, engineers, artists, spies, merchants or priests), building certain wonders or discovering certain technologies can improve the rate at which Great People are generated.  Great Generals are generated when a player's forces achieve a certain number of victories, and can be used either to give a small amount of extra experience to all units trained in a city, or a very high level of experience to one unit.  However, like other units, Great People of all kinds can be attacked and killed before the players can use them.<ref name="ignfaq"/>