The Landgraviate of Hesse-Kassel (), spelled Hesse-Cassel during its entire existence, was a state of the Holy Roman Empire. The state was created in 1567 when the Landgraviate of Hesse was divided upon the death of Philip I, Landgrave of Hesse. His eldest son William IV inherited the northern half of the Landgraviate and the capital of Kassel. The other sons received the Landgraviates of Hesse-Marburg, Hesse-Rheinfels and Hesse-Darmstadt.
During the Napoleonic reorganisation of the Empire in 1803, the Landgrave of Hesse-Kassel was elevated to an Electorate and Landgrave William IX became an Imperial Elector. Many members of the House of Hesse-Kassel served in the Danish military gaining high ranks and power in the realm due to the fact that many Landgraves were married to Danish princesses. Members of the family who are known to have served Denmark-Norway include Prince Frederik of Hesse-Kassel, Prince Frederick of Hesse-Kassel, and Prince Charles of Hesse-Kassel. It had two votes to the Reichstag: one for itself and one for Hersfeld Abbey. It was later occupied by French troops and became part of the Kingdom of Westphalia, a French satellite state. The Electorate of Hesse was restored at the end of the Napoleonic Wars, though by that time there was no longer an emperor to elect.
History
The Landgraviate of Hesse-Kassel was founded by William IV the Wise, the eldest son of Philip I. On his father's death in 1567, the Landgraviate of Hesse was divided into four parts. William IV received about half of the territory, with Kassel as his capital. Hesse-Kassel expanded in 1604 when Maurice, Landgrave of Hesse-Kassel inherited the Landgraviate of Hesse-Marburg from his childless uncle, Louis IV, Landgrave of Hesse-Marburg (1537–1604).
Thirty Years' War
In 1605, Maurice became Calvinist and entered the Thirty Years' War on the Protestant side. After being forced to cede some of his territories to Hesse-Darmstadt, Maurice abdicated in 1627 in favour of his son William V. His younger sons received appanages, which created several cadet lines in yet another partition of Hesse. William V allied himself with Gustavus Adolphus of Sweden and then France, losing most of Hesse-Kassel when Imperial troops invaded. He died in exile in 1637, leaving his widow Amalie Elisabeth of Hanau-Münzenberg to act as regent for their eight-year-old son William VI.
Amalie Elisabeth vigorously advanced the interests of Hesse-Kassel. After expelling Imperial troops from Hesse-Kassel, she sent troops to take the city of Marburg, which her father-in-law had lost to their Hesse-Darmstadt relatives. At the Peace of Westphalia in 1648, Hesse-Kassel was further rewarded with most of the County of Schaumburg and the newly secularized Hersfeld Abbey. Amalie Elisabeth also introduced the rule of primogeniture to prevent Hesse-Kasse from being divided again in the future. However, her health was ruined by the stresses of the war, and she died in 1651.
17th and 18th centuries
William VI, who came of age in 1650, was an enlightened patron of learning and the arts. He was succeeded by his son William VII, Landgrave of Hesse-Kassel, then an infant, who died in 1670. He was succeeded by his brother Charles I. Charles' chief claim to fame is that he hired out his soldiers to foreign powers as auxiliaries, as a means of improving the finances of his principality. William V was succeeded by Landgraves William VI and William VII. Frederick I of Sweden, the next landgrave, became by marriage King of Sweden. Although the Landgraviate was in personal union with Sweden from 1730 to 1751, the King's younger brother, Prince William, ruled in Kassel as regent until he succeeded his brother as William VIII.
On Frederick I's death in 1751, he was succeeded by his brother William VIII, who fought as an ally of Kingdom of Great Britain during the Seven Years' War. His successor, Frederick II, converted to Catholicism after a long line of Protestant Landgraviates. When the American Revolutionary War broke out, Frederick II leased Hessian troops to Great Britain for service in America.
End of the landgraviate
Following the reorganization of the German states during the German mediatisation of 1803, the Landgraviate of Hesse-Kassel was raised to the Electorate of Hesse and Landgrave William IX was elevated to Imperial Elector, taking the title William I, Elector of Hesse. The principality thus became known as , although still usually referred to as Hesse-Kassel.