Civilizations are playable factions, each of which represents a historical nation, empire or cultural group. Each civilization in Civilization VI has a unique ability and two unique components: a unit and a piece of infrastructure, which may be a building, a district, or a tile improvement. Vanilla Civilization VI included 18 different civilizations at the launch, with the Aztecs (19th) as a pre-order bonus that became available to everyone 90 days after the launch. The Poles, Australians, Persians, Macedonians, Nubians, Khmers, and Indonesians have since been added as DLC.