The Landgraviate of Hesse-Darmstadt was formed in 1567 following the division of the Landgraviate of Hesse between the four sons of Landgrave Philip I. The youngest son, George, received the Hessian lands in the former County of Katzenelnbogen. Hesse-Darmstadt was comprised of the northern province of Upper Hesse with Alsfeld, Giessen, Grünberg, the northwestern hinterland estates around Gladenbach, Biedenkopf and Battenberg and the southern Starkenburg territory with the Darmstadt residence, along with the exclave of Vöhl in Lower Hesse. The Landgraviate of Hesse-Kassel was given to the eldest son, William IV. Hesse-Marburg was given to Louis IV and Philip II became the Landgrave of Hesse-Rheinfels. Hesse-Darmstadt was a state of the Holy Roman Empire. In 1806, as a result of the Napoleonic Wars the landgraviate was elevated to the status of Grand Duchy, taking on the title of the Grand Duchy of Hesse. When Philip II died in 1583, the Hesse-Rheinfels line became extinct. In 1604, Louis IV of Hesse-Marburg died without an heir and sparked a rivalry between Hesse-Kassel and Hesse-Darmstadt that was further fuelled by religion.
The rivalry continued during the Thirty Years’ War where Hesse-Kassel sided with the Protestant estates and Hesse-Darmstadt sided with the Habsburg emperor. In 1627, Hesse-Darmstadt and Hesse-Kassel reached an agreement, but it was quickly revoked and resulted in the Siege of Dorsten. From 1645, Hesse-Darmstadt and Hesse-Kassel were engaged in a series of battles against each other and was settled on the eve of the 1648 Peace of Westphalia. Hesse-Darmstadt retained Biedenkopf and Giessen, while Hesse-Kassel obtained Upper Hesse territory. Hesse-Darmstadt inherited the estates of the Counts of Hanau-Lichtenberg in 1736, which was contested by Hesse-Kassel. The Reichsdeputationshauptschluss of 1803 authorized Hesse-Darmstadt in gaining a large section of territory, including the Duchy of Westphalia. Upon the dissolution of the Holy Roman Empire in 1806, and the dispossession of Elector Willian I of Hesse-Kassel, Louis X joined the Napoleonic Confederation of the Rhine and took the title of Grand Duke of Hesse. In 1815, the Duchy of Westphalia was ceded to Prussia. Hesse-Darmstadt was compensated with territory of the Rhine, including a fortress at Mainz. The northern half of the Grand Duchy of Hesse became a part of the North German Confederation, while the southern half remained outside the confederation. In 1871, the Grand Duchy became a constituent state of the German Empire. At the end of World War I, Grand Duke Ernst Ludwig, the last Grand Duke, was forced from his throne. The state was renamed the People’s State of Hesse. During World War II, the city of Darmstadt was the first to force Jewish stores to close. Darmstadt was largely destroyed by Allied bombing. At the end of World War II, the state was in the United States zone of occupation. It was then combined with Frankfurt am Main and the former Prussian province of Hesse-Nassau to form the new state of Hesse.