It was a principality (Landgraviate) of the Holy Roman Empire in the area of the today's Land of Hesse.
Maurice the Learned (1572–1632) was Landgrave of Hesse-Kassel from 1592 until 1627 when he abdicated in favour of his son William V (1602–1637), his younger sons receiving apanages which created several cadet lines of the house (Hesse-Rotenburg, Hesse-Eschwege and Hesse-Rheinfels), of which, with amalgamation, that of Hesse-Rheinfels-Rotenburg survived till 1834.
Ernest, who was a convert to the Roman Catholic Church, was a great traveller and a voluminous writer.
About 1700 his two sons, William (d. 1725) and Charles (or Karl) (d. 1711), divided their territories, and founded the families of Hesse-Rotenburg and Hesse-Wanfried.
[2] The latter family died out in 1755, when William's grandson, Constantine (d. 1778), reunited the lands except Rheinfels, which had been acquired by Hesse-Kassel in 1735, and ruled them as Landgrave of Hesse-Rotenburg.