the Prussian cities provided tax revenues sufficient to maintain a significant standing force composed of Teutonic Knights proper, their retinues, Prussian peasant levies, and German mercenaries. In 1402, the Luxembourg dynasty, which ruled the Margraviate of Brandenburg, reached an agreement with Poland in Kraków, according to which Poland was to purchase and re-incorporate the region of New March (Neumark). Later that year, however, the Luxembourgs gave the region in pawn to the Teutonic Order despite prior arrangements with Poland, and the Order kept it until Brandenburg redeemed it again in 1454 and 1455, respectively, by the Treaties of Cölln and Mewe. Though the possession of this territory by the Order strengthened ties between the Order and their secular counterparts in northern Germany, it exacerbated the already hostile relationship between the Order and Polish–Lithuanian union. In March 1407, Konrad died from complications caused by gallstones and was succeeded by his younger brother, Ulrich von Jungingen. Under Ulrich, the Teutonic State fell from its precarious height and became mired in internal political strife, near-constant war with Polish–Lithuanian union, and crippling war debts. Losses to Poland, Polish suzerainty In 1408, Conrad Letzkau served as a diplomat to Queen Margaret I and arranged that the Order sell Gotland to Denmark. In 1409, the Teutonic Order invaded Poland's Dobrzyń Land again, and the Polish–Lithuanian–Teutonic War broke out, in which the Teutonic Knights were supported by the Duchy of Pomerania, and the Polish-Lithuanian alliance was supported by Ruthenian, Tatar and Moldavian allies and auxiliary forces. Poland and Lithuania triumphed following a victory at the Battle of Grunwald (Tannenberg), which marked the start of the decline of the State of the Teutonic Order, and the rise of the Polish–Lithuanian union as a major power in Central and Eastern Europe. The Order assigned Heinrich von Plauen to defend Teutonic-held Eastern Pomerania (Pomerelia), who moved rapidly to bolster the defence of Marienburg Castle in Pomesania. Heinrich von Plauen was elected vice-grand master and led the Teutonic Knights through the Siege of Marienburg in 1410. Eventually von Plauen was promoted to Grand Master and, in 1411, concluded the First Treaty of Thorn with King Władysław II Jagiełło of Poland. The next major Polish–Teutonic war was fought in 1431–1435, after the Teutonic Knights invaded Poland again, and was ended in the Peace of Brześć Kujawski, which was favorable for Poland. In March 1440, gentry (mainly from Culmerland) and the Hanseatic cities