From 1402 to 1459 the state of the despots of Serbia had the role of a buffer zone between Hungary and the Ottoman Empire; its rulers being usually the vassals of both Ottoman sultans and kings of Hungary. That became obvious especially after the death of Despot George Branković in December 1456. The role of the nobility in the forthcoming period was significant because it constituted the largest part of Serbian army. Successor to Despot George, his son Despot Lazarus (1456-1458), set his heart on concluding a peace agreement with Sultan Mehmed II (1451-1481). His emissaries achieved that goal on 15 January at the Ottoman Porte. According to this treaty, the Serbian ruler had to pay 40.000 ducats annually to the Sultan and this tax was known as kharaj. However, this was less than during the reign of Despot George, as the Ottomans in 1455 had conquered the Southern part of the Serbian state including the rich mining town of Novo Brdo. Sources do not mention the obligation of sending auxiliary troops. Nevertheless, it is certain that Despot Lazarus was supposed to do so and the same did his predecessors. The noblemen were a majority of this kind of army. On the other side the new Serbian despot was embroiled in conflicts within the Kingdom of Hungary, which was the consequence of the murder of his cousin Ulrich II Cilli. He supported King Ladislas V (1440-1457) against the Hunyadi. With the assistance of royal supporters, Despot Lazarus occupied Kovin (Kewe), Laslovar, Haram, Požežena and Dombo, the towns in south-western Banat in the April 1457. The advance of the Serbian army through Banat ended on 25 May, when it was defeated by the Hunyadi's troops. Despite being repressed, the Serbian ruler kept control over the mentioned towns on the left bank of the River Danube until his death. Simultaneously, the Brankovići were experiencing some inner disputes. The first disagreement broke out between Irene, the widow of Despot George, and Despot Lazarus. Gregory, oldest son of Despot George, who was blind, provided the support for his mother. During this conflict, Irene died on 3 May 1457 in the town of Rudnik. Afterwards, her brother Thomas and her children, Gregory and Mary, left Serbia to come to the Sultanate.