Luther, a professor of theology in Germany, believed that faith alone led to salvation, which could be granted only by God. He challenged the claims of Pope Leo X and his bishop in Germany that individuals could achieve salvation by buying indulgences, which were documents that absolved the buyer of sin. The church profited enormously from these sales, but they suggested that God’s grace could be purchased. In 1517 Luther wrote an extended argument against indulgences and sent it to the local bishop. Although intended for learned clerics and academics, his writings soon gained a wider audience.

Luther’s followers, who protested Catholic practices, became known as Protestants. His teachings circulated widely through sermons and printed texts, and his claim that ordinary people should read and reflect on the Scriptures appealed to the literate middle classes. Meanwhile his attacks on indulgences and corruption attracted those who resented the church’s wealth and priests’ lack of attention to their flock. In Switzerland, John Calvin developed a version of Protestantism in which civil magistrates and reformed ministers ruled over a Christian society. According to Calvinist beliefs, God was all-knowing and absolutely sovereign, while man was weak and sinful. Calvin argued that God had decided at the beginning of time who was saved and who was damned. Calvin’s idea, known as predestination, energized Protestants who understood salvation as a gift from an all-knowing God in which human “works” played no part.

The Protestant Reformation quickly spread through central and northern Europe. England, too, came under the influence of Protestantism in the 1530s, although for different reasons. When the pope refused to annul the marriage of King Henry VIII and Catherine of Aragon, Henry denounced papal authority and established the Church of England, or Anglicanism, with himself as “defender of the faith.” Despite the king’s conversion to Protestantism, the Church of England retained many Catholic practices.

In countries like Spain and France with strong central governments and powerful ties to the Catholic Church, a strong Catholic Counter-Reformation largely quashed Protestantism. At the same time, Catholic leaders initiated reforms to counter their critics. In 1545 Pope Paul II called together a commission of cardinals, known as the Council of Trent (1545–1563), to address contentious issues such as corrupt bishops and priests, indulgences, and other financial abuses. The council initiated reforms, such as the founding of seminaries to train priests and the return of monastic orders to their spiritual foundations.

Religious upheavals in Europe contributed significantly to empire building in North America. Protestant and Catholic leaders urged followers to spread their faith across the Atlantic, while religious minorities sought a safe haven in North America. Just as important, political struggles erupted between Catholic and Protestant rulers in Europe following the Reformation. The politicization of religious divisions resulted in peasant unrest, economic crises, and military conflicts that pushed (or forced) people to seek new opportunities in the Americas. Thus in a variety of ways, religious transformations in Europe fueled the construction of empires in America.