The Great Crusade was a significant military campaign initiated by the Emperor of Mankind in the fictional universe of Warhammer 40,000. Its primary goal was to reunite humanity across the galaxy, bringing various human colonies under the control of the Imperium of Man. This campaign involved the deployment of the Adeptus Astartes, also known as Space Marines, who were genetically enhanced super-soldiers. During the Great Crusade, the Emperor sought to eliminate threats to humanity, including alien species and heretical factions. The campaign was marked by numerous battles and the discovery of lost human worlds, ultimately leading to the establishment of the Imperium as a dominant force in the galaxy.