Mongolia is the purest conquest civilization of the Exploration Age — capturing enemy Settlements directly replenishes your Cavalry, turning every successful siege into fuel for the next one.
Its unique ability grants the strongest Cavalry unit you can currently train whenever you capture an opposing Settlement, at the cost of reduced Production toward Settlers — a mechanic that rewards conquering existing cities over founding new ones. A separate tier adds increased Combat Strength for Cavalry units generally.
The Keshig is a unique Ranged Cavalry unit with increased Movement that ignores Zone of Control, and heals a set amount of HP whenever it defeats an enemy — letting a Mongol cavalry army stay on the offensive far longer than most.
The Ortöö is a unique Improvement that restores full Movement to any unit entering the tile — genuinely useful for sustaining a fast-moving offensive across long distances. The associated Wonder, Erdene Zuu, grants Culture and rewards training Cavalry units with additional Culture equal to a percentage of their cost; it must be built on Flat Plains, Tundra, or Desert.