During which historical conflict is the first Assassin's Creed game mainly set?

The first Assassin's Creed game is mainly set during the Third Crusade.

Its historical sections take place in the late twelfth century, when Altaïr Ibn-La'Ahad operates in the Holy Land. The game depicts several major centers connected with the conflict, including Masyaf, Jerusalem, Acre, and Damascus.

The Third Crusade lasted from 1189 to 1192 and involved European rulers such as Richard I of England, Philip II of France, and the Holy Roman Emperor Frederick Barbarossa. Saladin led the Ayyubid forces opposing the crusaders. The game uses this real setting as the backdrop for its fictional Assassin-Templar storyline.

Assassin's Creed does not present a documentary account of the crusade. Its characters, secret organizations, and many events are fictionalized, while some historical figures and locations are incorporated into the narrative.