In which historical conflict is the original Assassin's Creed primarily set?

The original Assassin's Creed is primarily set during the Third Crusade.

Its historical storyline takes place in 1191, when Altaïr Ibn-La'Ahad carries out missions in the Holy Land. The game visits Masyaf, Jerusalem, Acre, and Damascus, placing its fictional Assassin-Templar conflict against the political and military background of the Third Crusade.

The real Third Crusade lasted from 1189 to 1192 and followed the capture of Jerusalem by Saladin in 1187. Historical figures such as Richard the Lionheart and Saladin appear in the game's world, although the central conspiracy and many character relationships are fictionalized.

The game is not set during the First Crusade, even though the series often uses a broad medieval setting. Nor is it primarily about the later Crusades. Its date, locations, and major historical backdrop specifically connect it to the Third Crusade.