Martin Luther's 95 Theses Ignited the Protestant Reformation in 1517

On October 31, 1517, Martin Luther posted his Ninety-Five Theses on the doors of Schlosskirche in Wittenberg, challenging the Roman Catholic Church's sale of indulgences. This act, originally intended as a call for debate, sparked the Protestant Reformation. Luther condemned the practice of selling divine forgiveness, particularly criticizing Pope Leo X's fundraising for St. Peter's Basilica through indulgences sold in Germany by Johann Tetzel. The theses questioned papal authority and the theological basis of indulgences, arguing salvation came through faith alone (sola fide) rather than financial transactions. Luther's defiance escalated when he refused to recant before Cardinal Cajetan in 1518 and during the Diet of Worms in 1521, where he famously declared he could not go against his conscience. Excommunicated by Pope Leo X in January 1521 and declared an outlaw by Holy Roman Emperor Charles V in May 1521, Luther translated the New Testament into German while hiding at Wartburg Castle. His ideas spread rapidly across Europe, influencing reformers like Ulrich Zwingli and John Calvin, and permanently divided Western Christianity. The Reformation had profound political, economic, and cultural impacts, with Lutheranism dominating northern Europe by the mid-16th century. Earlier critics like William of Ockham, John Wycliffe, Jan Hus, Lorenzo Valla, and Desiderius Erasmus had also denounced church abuses, but Luther's actions triggered a lasting schism.