Which Assassin's Creed game introduced the Brotherhood system that lets Ezio recruit and command other Assassins?

Assassin's Creed Brotherhood introduced the system that lets Ezio recruit and command other Assassins.

Released in 2010, Brotherhood continues Ezio Auditore's story after Assassin's Creed II. Its central setting is Rome, where the Borgia family controls much of the city and the Assassin presence has been weakened. Ezio rebuilds the local Brotherhood by recruiting civilians and training them for missions.

Recruited Assassins can be sent to assignments across Europe or called into missions to assist Ezio. As they gain experience, they become more effective and can eventually reach the rank of Master Assassin. The system gives the title its thematic focus: Ezio is no longer working mainly as a lone operative.

Assassin's Creed II includes allies and equipment upgrades, but it does not contain this same recruit-and-command Brotherhood feature. Revelations continues Ezio's later life and includes related systems, but Brotherhood is the game that introduced the mechanic.