 Complete the following phrase:  In 1427, Stefans successor Đurađ Branković, returning Belgrade to the Hungarian king, made Smederevo his new capital. Even though the Ottomans had captured most of the Serbian Despotate, Belgrade, known as Nándorfehérvár in Hungarian, was unsuccessfully besieged in 1440 and 1456. As the city presented an obstacle to the Ottoman advance into Hungary and further, over 100,000 Ottoman soldiers 