In 1247, as Heinrich Raspe, Landgrave of Thuringia, died without issue, conflict arose about the future of Thuringia and Hesse. The succession was disputed between Heinrich Raspe's nephew and his niece: Sophie was the daughter of Heinrich Raspe's brother Ludwig IV and claimed the territories on behalf of her son Henry, while Henry the Illustrious, margrave of Meissen, was the son of Heinrich Raspe's sister Jutta. Another competitor were the Archbishops of Mainz, who could claim Hesse was a fiefdom of the archbishop and now, after the extinction of the Ludowingians, demanded its return to them. Sophia, supported by the Hessian nobility, succeeded in retaining Hesse against her cousin, who in 1264 accepted the division of the Ludowingian inheritance: Henry of Meissen received Thuringia, while Sophia's son Heinrich would inherit Hesse. In the following year, the Archbishop Werner II von Eppenstein acceded to this outcome in the Treaty of Langsdorf, accepting Henry as his liege-man and Landgrave of Hesse.
At this time, the landgraviate of Hesse consisted of the region between Wolfhagen, Zierenberg, Eschwege, Alsfeld, Grünberg, Frankenberg and Biedenkopf. In the same year, Henry acquired a part of the county of Gleiberg with Gießen from the Counts palatine of Tübingen. The landgraviate was centred on the towns of Kassel, where Henry took up his residence since 1277, and Marburg, where his grandmother Saint Elisabeth was buried and where Henry built the Castle Marburg.
Struggle for possession of Naumburg
Henry again got into conflict with his liege-lord, the Archbishop, about the possession of Naumburg. On behalf of the Archbishop, Henry was outlawed in 1274 by King Rudolf I of Habsburg, but after Henry had supported Rudolph in the war against Otakar II of Bohemia and had helped to conquer Vienna 1276, Rudolph reinstated Henry. In 1290 Henry defeated the Archbishop in the battle of Fritzlar and could henceforth maintain his territory.
Though Henry never relinquished his own claim on Brabant, he supported his nephew John of Brabant against Guelders and Luxembourg in the Limburg succession war.
Elevation to prince of the realm
On 12 May 1292, Henry was made a Reichsfürst (prince of the realm) by King Adolf of Nassau, freeing Hesse of the supremacy of the Archbishop of Mainz. Henry was bestowed with Eschwege and the Boyneburg (with Sontra), strengthening his position in Hesse. By skillful diplomacy he gained the cities of Sooden-Allendorf, Kaufungen, Witzenhausen, Immenhausen, Grebenstein, Wanfried, Staufenberg, Trendelburg and Reinhardswald.
In 1263 Henry had married Adelheid of Brunswick, daughter of Duke Otto of Brunswick, who bore him four daughters and the sons Henry ("the Younger") and Otto. After Adelheid's death in 1274, Henry had married Mechthild, daughter of Dietrich VI, Count of Cleves, who bore him another four daughters and the sons John and Louis.
Uncertainty over succession
In 1292 internal conflict arose about the question of Henry's successor. Mechthild of Cleves demanded on her sons receiving a share of the heritage, while Henry and Otto, Henry's sons by his first wife, insisted on excluding their half-brothers from the inheritance. This led to civil war lasting throughout the rest of Henry's lifetime.
Henry died in Marburg during the conflict, and was buried there in St. Elisabeth's Church, which became the gravesite of the succeeding Landgraves for several more centuries. After his death, the inheritance was divided between Otto, who received Upper Hesse (Oberhessen) around Marburg, and John, who received Lower Hesse (Niederhessen), centred on Kassel. John's younger brother Ludwig had entered the clergy and became bishop of Münster in 1310.
