Nevertheless, Albert's plans to re-unite the former Duchy of Franconia under his rule failed: in 1443, he formed a league directed mainly against the Imperial City of Nuremberg, over which his late father had formerly exercised the rights of burgrave. It was not until 1448, however, that he found a pretext for attack. After initial military successes in the First Margrave War, he was defeated at the Battle of Pillenreuther Weiher, resulting in the Treaty of Bamberg (22 June 1450), which forced Albert to return all of the conquered territory and to recognize the independence of Nuremberg and its associated towns.