Which Assassin's Creed game introduced the recruitable Brotherhood system in Renaissance Rome?

Assassin's Creed Brotherhood introduced the recruitable Brotherhood system in Renaissance Rome.

Released in 2010, Brotherhood lets Ezio Auditore find civilians in Rome who are being oppressed by Borgia forces and recruit them into the Assassin Brotherhood. Recruits can be trained, assigned to missions across Europe, and summoned during gameplay to assist Ezio. Their abilities improve as they gain experience, creating a progression system tied directly to the narrative.

The mechanic reflects Ezio's role as a leader rather than only as an individual operative. Rome itself is also part of the rebuilding process: Ezio liberates districts, restores shops and landmarks, and weakens Borgia control. These systems make the city feel like an organization-wide campaign instead of a sequence of isolated assassination contracts.

The game is sometimes confused with Assassin's Creed II because both star Ezio and share Renaissance Italian settings. Assassin's Creed II established Ezio's origin, while Brotherhood expanded his leadership role and centered its campaign on Rome. Revelations continued his story but moved the main historical setting to Constantinople.