John died in 1277, the regency was held by his brother, Albert, on behalf of John's underage son, Otto the Strict, before Otto assumed power himself in 1282. Otto asserted his rule through the prosecution of numerous feuds against the lesser nobility, which enabled him to achieve consolidate his ducal authority within the state. He also continued the "systematic acquisition policy" (planmässige Erwerbspolitik) in the Lüneburg principality that had operated since the time of Otto the Child, "rounding off the Lüneburg allodial estate" (Arrondierung des Lüneburger Allodialbesitzes) through the purchase of numerous lands and rights, including those of Bleckede and Hitzacker, the County of Dannenberg and the County of Wölpe. Duke Otto was followed by his sons, Otto III of Lüneburg and William of Lüneburg. The instruction issued by their father in 1318 whereby the principality would be divided after his death between Otto III and his brother, William II, was ignored by the brothers and in 1330 they assumed joint control of an undivided state. The focus of their rule in the early years was a further territorial consolidation of the principality. For example, they were able to considerably increase their estate in the region of Gifhorn through the purchase of the village of Fallersleben, the County of Papenteich and Wettmarshagen. Another top priority was their political support for the towns, which were striving to develop themselves economically. For instance, the merchants of Lüneburg benefited considerably from work to make the River Ilmenau navigable between Lüneburg and Uelzen and from trade agreements between the Lüneburg princes and the dukes of Saxe-Lauenburg. The two brothers reigned jointly until the death of Otto III in 1352, leaving William in sole charge until his own death in 1369. Lüneburg War of Succession When William II of Lüneburg died in 1369 without a son, the first house of Lüneburg became extinct. According to Welf house rules and the desire of William, Duke Magnus II Torquatus of Brunswick would have been the rightful heir. Emperor Charles IV, however, considered it an imperial fiefdom, however, and granted the principality to Albert of Saxe-Wittenberg and his uncle Wenceslas, thus precipitating the Lüneburg War of Succession. The town of Lüneburg supported the Wittenbergs and took the opportunity to escape from the immediate influence of the duke, destroying the ducal castle on the Kalkberg on 1 February 1371 and forcing him to relocate his residence to Celle. An