During the Thirty Years' War, Calvinist Hesse-Kassel proved to be Sweden's most loyal German ally. Landgrave William V and, after his death in 1637, his widow Amelia of Hanau, a granddaughter of William the Silent, as regent supported the Protestant cause and the French and Swedes throughout the war and maintained an army, garrisoning many strongholds, while Hesse-Kassel itself was occupied by Imperial troops.