In the two millennia of its history Christianity has been divided by schism and roiled by heresy, based on doctrinal and organizational differences. Today there are three broad divisions, Roman Catholic, Orthodox Eastern, and Protestant; but within the category of Protestantism, there is a particularly large number of divergent denominations. Because of the complexity of these differences this article will describe the history of Christianity only to 1054, when the schism between Eastern and Western churches became final. Separate articles detail the history and doctrines of the Roman Catholic Church and Orthodox Eastern Church and of the other churches of ancient origin, the Armenian Church, the Coptic Church (see Copts), the Jacobite Church, and the Nestorian Church. In the 16th cent. another major schism took place in the Western Church with the Protestant Reformation. For the Protestant churches, see Protestantism and articles on the separate churches. For the 20th-century movement that seeks to end the divisiveness in Christianity and achieve reunion, see ecumenical movement.