Which Assassin's Creed game was the first main series title released after Assassin's Creed III?

Assassin's Creed IV: Black Flag was the first main series title released after Assassin's Creed III.

Assassin's Creed III launched in 2012, and Black Flag followed in 2013. Although its title uses the number IV, Black Flag tells a story set earlier than Assassin's Creed III, during the Golden Age of Piracy in the early eighteenth century. This makes its release order and historical chronology different.

Black Flag stars Edward Kenway and expands the naval elements introduced in Assassin's Creed III into a central gameplay system. It was released for multiple platforms, including PlayStation 3, Xbox 360, Wii U, Windows, PlayStation 4, and Xbox One.

Assassin's Creed Rogue was also released in 2014, while Unity followed later that year. Liberation was first released as a PlayStation Vita title in 2012 and is a spin-off rather than the next main numbered entry. The answer concerns release order, not the chronological order of the fictional history.