The subtitle is Brotherhood for the 2009 game Assassin’s Creed: Brotherhood.
Brotherhood continues Ezio Auditore’s story after Assassin’s Creed II and places much of its campaign in Rome. Ezio works to dismantle the Borgia family’s power and rebuild the Assassin Brotherhood in Italy, making recruitment and organization important parts of the game.
The title introduced the series’ first major multiplayer mode and expanded the idea of calling recruited Assassins into missions. It also continues the modern-day storyline involving Desmond Miles and his companions.
Revelations is the later Ezio game set mainly in Constantinople, while Liberation follows Aveline de Grandpré in eighteenth-century Louisiana. Brotherhood should therefore be identified by its Rome-focused campaign and its emphasis on rebuilding the Brotherhood rather than by the broader presence of Ezio alone.