The Crusading movement was a major religious, political, and military endeavour of the Middle Ages, generally dated from the Council of Clermont (1095), at which Pope Urban II proclaimed the First Crusade, an armed expedition in support of Eastern Christians under Muslim rule. He framed it as a form of penitential pilgrimage. By this point, papal authority had grown through church reforms, and tensions with secular rulers encouraged the notion of holy war—combining classical just war theory, biblical precedents, and Augustine's teachings on legitimate violence. Armed pilgrimage aligned with the era's Christocentric and militant Catholicism, sparking widespread enthusiasm. Western expansion was further enabled by economic growth, the decline of older Mediterranean powers, and Muslim disunity. These factors allowed crusaders to seize territory and found four Crusader states in the Levant, whose defence inspired successive Crusades. The papacy also launched crusading campaigns against other targets—Muslims in Iberia, paganism in the Baltics, and other opponents of papal authority.