The Crusades were multiple campaigns of a religious war fought by most of Christian Europe against different enemies. They were fought mainly against the Muslims, though some campaigns were also aimed at pagan Slavs, Jews, Russian and Greek Orthodox Christians, Mongols, Cathars Hussites and political enemies of the Popes. Basically anyone not Christian and under the Pope would get attacked by Crusaders. To get the Crusaders for the actual fighting the Pope gave an indulgence for past sins for anyone who took the vow to be a Crusader.

The original goal of the Crusades was to retake Jerusalem and the Holy land from the Muslims. The Crusades also campaigned in territories controlled by pagans, heretics, or people who had been banned for many different reasons.

The Crusades had far-reaching political, economic, and social impacts, some of which have lasted into contemporary times. Because of bickering amongst the Christian kingdoms and political powers, some of the crusades were actually diverted from what they were suppose to do and used as regular soldiers. After the Ninth Crusade the Christian powers in Europe stopped them all together.