Which Assassin's Creed game introduced the Assassin Brotherhood's Rome-based guild management system?

Assassin's Creed: Brotherhood introduced the series' Rome-based guild management system.

Released in 2010, Brotherhood continues Ezio Auditore's story after Assassin's Creed II. Ezio operates primarily in Rome, where the Borgia family controls much of the city. He recruits civilians, trains them as Assassins, and calls on them during missions.

The recruitment system is tied to the game's wider effort to rebuild the Assassin Brotherhood. Players can send recruits on missions, improve their skills, and use them to support Ezio in combat or assassination tasks.

Brotherhood also introduced the series' first major multiplayer component, in which players hunted one another using different Templar characters. It is distinct from Revelations, which later concluded Ezio's main story in Constantinople.