In 1568 with the death of Landgrave Philip I, the Landgraviate of Hesse (), a German Principality of the Holy Roman Empire, was divided among his sons. With the extinction of the Hesse-Marburg and Hesse-Rheinfels lines by 1604, Hesse-Darmstadt, along with Hesse-Kassel, became one of the two Hessian states. While Hesse-Kassel converted to Calvinism and became one of the most zealous exponents of the Protestant cause in the Thirty Years' War, Landgrave George II remained a strict Lutheran and maintained a close alliance with Saxony, which led to a pro-Habsburg policy after 1642.