In this period, during the reigns of despots Stefan Lazarević (1389-1427) and Đurađ Branković (1427-1456), Serbia cooperated with Hungary. In the second half of the 15th century, the Ottoman conquest became a major issue in the European politics. Taking Crusades as a mold, both the rulers of the European states and the church leaders forged a myriad of plans for researching and repelling the Turks. However, when the time for the serious preparations would come, the funding would turn out to be a major problem. As the feudal states engaged more and more in the mutual wars, there was no money for the operations on the east of the continent. Being on the frontline of the Ottoman expansion, Serbia and Hungary formed an alliance. The greatest fruit of this collaboration was the joint 1443 campaign which resulted in the liberation of Serbia and its reestablishment as a state after it was conquered by the Ottomans in 1439.