 Complete the following phrase:  In 1427, Stefans successor Đurađ Branković had to return Belgrade to the Hungarian king, and Smederevo became the new capital. Although the Ottomans captured most of the Serbian Despotate, Nándorfehérvár  as it was known in the Kingdom of Hungary  was unsuccessfully besieged in 1440 and again in 1456. As it presented an obstacle to their advance into Hungary and further Europe, over 100,000 Ottoman soldiers launched the 1456 