The Protestant Reformation began in 1517 when Martin Luther wrote his 95 Theses criticizing the Catholic Church's practice of selling indulgences. Luther studied the Bible and concluded that faith alone, not good works or sacraments like confession, were necessary for salvation. When the pope excommunicated Luther in 1521, many German princes adopted Lutheranism, seeing it as a way to assert independence from the Catholic Church and Holy Roman Empire. Luther's writings spread his message of reform and Protestantism took hold across Germany and Scandinavia, though Luther himself struggled with the Peasants' War and maintaining control over the growing movement.