Civilization IV: Warlords is the first official expansion pack for well-known video game Civilization IV. The game adds new features into original game such as a new category called Great Generals which can join a city as a Great Military Instructor, which gives +2 experience points to any military unit created in the city or creates a Military Academy, which boosts military unit production by 50%. Also, the game offers the ability to institute vassal states, which lets player to take up other empires as vassals. When an empire becomes a vassal, it loses the ability to declare war and make peace independently. Warlords offers new civilizations including Carthage, the Celts, Korea, the Ottoman Empire, the Vikings and the Zulu, and four new leaders for existing civilizations. There are also eight new scenarios, six new civilizations which can be played in single-player as well as in multiplayer mode, ten new leaders, three new leader traits, unique buildings for each civilization, three new wonders, new units, resources and improvements, core gameplay tweaks and additions and inclusion of all patches released for original game.