Which game introduced the Assassin's Creed series' pirate-focused Caribbean setting?

Assassin's Creed IV: Black Flag introduced the series' pirate-focused Caribbean setting.

Released in 2013, Black Flag places Edward Kenway in the Caribbean during the early eighteenth century, a period associated with the Golden Age of Piracy. Players sail between locations including Havana, Nassau, and Kingston, using Edward's ship, the Jackdaw, for travel, combat, and exploration.

Naval gameplay had already appeared in Assassin's Creed III, but Black Flag made sailing and ship-to-ship combat central to the entire experience. The game combines that maritime structure with traditional assassination missions, underwater exploration, treasure hunting, and encounters with historical pirates.

Assassin's Creed Rogue also uses extensive naval gameplay and visits parts of the North Atlantic and Caribbean, but it was released after Black Flag. Freedom Cry is a downloadable expansion and standalone release built from Black Flag's technology, not the first main game to introduce the Caribbean pirate format.