Hesse-Kassel

The Landgraviate of Hesse-Kassel (Landgrafschaft Hessen-Kassel) or Hesse-Cassel was a state in the Holy Roman Empire under Imperial immediacy that came into existence when the Landgraviate of Hesse was divided in 1567 upon the death of Philip I, Landgrave of Hesse. His eldest son William IV inherited the northern half and the capital of Kassel. The other sons received the Landgraviate of Hesse-Marburg, the Landgraviate of Hesse-Rheinfels and the Landgraviate of Hesse-Darmstadt.

The Landgrave of Hesse-Kassel was elevated to Prince-elector during the reorganization of the Empire in 1803, in the midst of the Napoleonic wars. The Electorate of Hesse (Kurfürstentum Hessen), also known as Electoral Hesse (Kurhessen), was later occupied by French troops and became part of the Kingdom of Westphalia, which was a French satellite state. The Electorate of Hesse was reestablished in 1813 and became a member state of the German Confederation. It was finally annexed by the Kingdom of Prussia in 1866 after the Austro-Prussian War and subsequently became the Province of Hesse-Nassau.

17th and 18th centuries
Since the early years of the Reformation the House of Hesse was clearly Protestant, with only a few exceptions. Landgraves Philip I, William V, and Maurice married descendants of King George of Bohemia. From William VI onwards, mothers of the heads of Hesse-Kassel were always descended from William the Silent, the leader of the Dutch to independence on basis of Calvinism.

The Landgraviate of 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).

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.

William V was succeeded by Landgraves William VI and William VII. Under King Frederick I of Sweden, Hesse-Kassel was in personal union with Sweden from 1730–51. But in fact the King's younger brother, Prince William, ruled in Kassel as regent until he succeeded his brother, reigning as William VIII until 1760.

Although it was a fairly widespread practice at the time to rent out troops to other princes, it was the Landgraves of Hesse-Kassel who became infamous for hiring out contingents of their army as mercenaries during the 17th and 18th centuries. Hesse-Kassel maintained 7% of its entire population under arms throughout the eighteenth century. This force served as a source of mercenaries for other European states. Frederick II, notably, hired out so many troops to his nephew King George III of Great Britain for use in the American War of Independence, that "Hessian" has become an American slang term for all German soldiers deployed by the British in the War. Frederick used the revenue to finance his opulent lifestyle. One of these regiments that saw service in America was the Musketeer Regiment Prinz Carl.

During the 17th century, the landgraviate was internally divided for dynastic purposes, without allodial rights, into:
 * the Landgraviate of Hesse-Rotenburg (1627–1834)
 * the Landgraviate of Hesse-Wanfried-(Rheinfels) (1649–1755)
 * the Landgraviate of Hesse-Philippsthal
 * Landgraviate of Hesse-Philippsthal-Barchfeld

These were reunited with the Landgraviate of Hesse-Kassel when each particular branch died out without issue.

19th century
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 Kurhessen, although still usually referred to as Hesse-Kassel.

In 1806, William I was dispossessed by Napoleon Bonaparte for his support of the Kingdom of Prussia, and Kassel became the capital of a new Kingdom of Westphalia with Napoleon's brother Jérôme Bonaparte as king. The elector was restored following Napoleon's defeat in 1813, and although the Holy Roman Empire was now defunct, William retained his title of Elector, as it gave him pre-eminence over his cousin, the Grand Duke of Hesse. From 1813 onwards, the Electorate of Hesse was an independent country and, after 1815, a member of the German Confederation.

William's grandson, Elector Frederick William, sided with the Austrian Empire in the Austro-Prussian War, and after the Prussian victory his lands were annexed by Prussia in 1866. Along with the annexed Duchy of Nassau and Free City of Frankfurt, Hesse-Kassel became part of the new Province of Hesse-Nassau of the Kingdom of Prussia.

20th century
In 1918, Hesse-Nassau became part of the Free State of Prussia until 1944. From 1944–45 as part of Nazi Germany, it was divided into the Prussian provinces of Kurhessen and Nassau. From 1945–46, it was renamed Greater Hesse (Großhessen) and was part of the US occupation zone in Germany. From 1946 onwards, it was reorganised into the State of Hesse, a federal state of West Germany.

In 1918, Prince Frederick Charles of Hesse, younger brother of the head of the house and a brother-in-law of Emperor William II, was elected by the pro-German Finnish government to be King of Finland, but he never reigned.

In 1968, the head of the House of Hesse-Kassel became the head of the entire House of Hesse due to the extinction of the House of Hesse-Darmstadt.

Other uses
The village of Hessen Cassel, Indiana near Fort Wayne, founded by German immigrants, is named for the Landgraviate of Hesse-Kassel.