Papal corruption during the Renaissance provided the background for the Protestant Reformation and alienated many followers of the established church. Martin Luther and his colleagues entered upon a basic theological revolution, reacting in part to the state of the papacy. They denounced the whole accepted view of God's relation to humanity and began a movement that split the Western Church.
Although reformation within the church began in the 1520s, papal involvement did not begin until the election (1534) of Paul III (see Counter Reformation). The Council of Trent (1545–47, 1551–52, 1562–63; see Trent, Council of) undertook to lay out the new definitions and regulations that reconstructed the church, including the papacy. The other major work of the 16th-century popes was the new development of foreign missions, which, as in ancient times, enhanced papal prestige. Of the several orders concerned with reform and missions, the Jesuits (see Jesus, Society of) were the best known. The 16th cent. also saw the stabilization of the Papal States as they would remain until the 19th cent.