Answer: Holy war, any war fought by divine command or for a religious purpose. The concept of holy war is found in the Bible (e.g., the Book of Joshua) and has played a role in many religions. See crusade; jihad.
The aim was to capture the sacred places in the Holy Land from the Muslims who lived there, so it was intended as a war to right wrongs done against Christianity. The first Crusade was started by Pope Urban II in 1095.