The Protestant Reformation was sparked by Martin Luther's Ninety-Five Theses, which he posted on the door of the Wittenberg Castle Church in 1517. Luther criticized the Roman Catholic Church's practices, particularly the sale of indulgences, and called for a return to biblical teachings. His actions challenged the authority of the Church and initiated a religious and political upheaval that led to the formation of various Protestant denominations. The Reformation ultimately changed the course of European history, resulting in significant theological, social, and political transformations, including the rise of religious pluralism and the end of the Catholic Church's monopoly on Christianity in Europe.