The Thirty Years' War

The Defenestration of Prague by Václav Brožík

In 1555, Holy Roman Emperor Charles V had granted the Peace of Augsburg, in which he allowed each member state of the Holy Roman Empire to choose whether it would follow Roman Catholicism or Lutheranism.

However, in 1619, Charles' grand-nephew became Emperor Ferdinand II, and sought to unify Christendom by reversing his predecessors' religious policies. This caused many of the states in the north to unify against Ferdinand, forming the Protestant Union. Bohemia went into revolt with The Defenestration of Prague, when local Protestants threw three of the emperor's officials out of a third-story window (although all three men survived the 70-foot fall.)

In defense of the Empire, Bavaria attacked the rebels in Bohemia. Saxony and Sweden, which were both Lutheran, then attacked Bavaria to defend Bohemia. Spain then said they were entering the war to defend Austria, because Emperor Ferdinand and Spanish King Philip III were both Habsburgs (but really, Spain just wanted an excuse to march into the Netherlands and crush the Dutch, who were allied with the Protestants.)

Now surrounded by Spanish and German armies, France entered the conflict on the side of the Protestants. Although France was a majority Catholic country, it was ruled by the House of Bourbon, who were rivals to the Habsburgs.

Conflict continued across Europe until the 1648 Peace of Westphalia. In this treaty, religious freedom was granted for Catholics, Lutherans, and now Calvinists, all across Europe. The Netherlands became a formally independent country, and it is often said that Westphalia was the birthplace of the concept of a sovereign state.

When it was all over, the Thirty Years' War had resulted in over eight million deaths (mostly from the devastation of trade and infrastructure, rather than from actual combat), the worst conflict until the 20th century.