The Crusaes were a series of military conflicts of a religious character waged by much of Christian Europe against external and internal threats; there was also rioting. Crusades were fought mainly against Muslims, though campaigns were also directed against pagan Slavs, Jews, Russian and Greek Orthodox Christians, Mongols, Cathars, Hussites, and political enemies of the popes. Crusaders took vows and were granted an indulgence for past sins.