The Protestant Reformation

The Protestant Reformation (1517–c. 1648) was one of the most consequential events in Western history. What began as a German monk's theological protest against the sale of indulgences grew into a continental movement that permanently shattered the unity of Western Christianity, triggered devastating religious wars, and reshaped European politics, culture, and thought.

Martin Luther's posting of the 95 Theses in 1517 challenged the Catholic Church's practice of selling indulgences — promises of reduced time in purgatory in exchange for cash payments. Luther's deeper argument was theological: salvation came through faith alone (sola fide), based on scripture alone (sola scriptura), by grace alone (sola gratia). These principles denied the Church's role as necessary mediator between God and humanity — a revolutionary challenge to an institution that had dominated European life for a millennium.

The Reformation spread rapidly, aided by the printing press (which made Luther's writings the first mass-media phenomenon), German princes seeking independence from papal and imperial authority, and genuine popular religious fervor. John Calvin in Geneva, Huldrych Zwingli in Zurich, and Henry VIII in England created alternative Protestant traditions. The resulting religious division — Catholic south, Protestant north — defined European politics for centuries and contributed to the devastating Thirty Years' War (1618–1648), which killed perhaps a third of the German population.