Much of the period is marked by conflict between the Muslim and Christian states of Spain, referred to as the Reconquista, or the Reconquest (i.e., The Christians "reconquering" their lands as a religious crusade). The border between Muslim and Christian lands wavered southward through 700 years of war, which marked the peninsula as a militarily contested space. The medieval centuries also witnessed episodes of warfare between Spain's Christian states. Wars between the Crown of Aragon and the Crown of Castile were sparked by dynastic rivalries or disagreements over tracts of land conquered or to be conquered from the Muslim south.