 When, in 1604, the childless Landgrave Louis IV of Hesse-Marburg died at Marburg Castle, a succession dispute to his lands, along with the sectarian differences between Calvinist Hesse-Kassel and Lutheran Hesse-Darmstadt, led to a bitter, decades-long rivalry.Because the University of Marburg had become Calvinist under the rule of Landgrave Maurice of Hesse-Kassel, his cousin Louis V of Hesse-Darmstadt founded the Lutheran University of Giessen in 1607.The inheritance conflict was continued in the broader contest of the Thirty Years' War, in which Hesse-Kassel sided with the Protestant estates and Hesse-Darmstadt sided with the Habsburg emperor.