 Complete the following phrase:  The crumbling Serbian Empire under Uroš the Weak offered little resistance to the powerful Ottomans. In the wake of internal conflicts and decentralization of the state, the Ottomans defeated the Serbs under Vukašin at the Battle of Maritsa in 1371, making vassals of the southern governors; soon thereafter, the Emperor died. As Uroš was childless and the nobility could not agree on a rightful heir, the Empire continued to be ruled by semi-independent provincial lords, who often were in feud with each other. The most powerful of these, Lazar Hrebeljanović, a Duke of present-day central Serbia which had not yet come under Ottoman rule, stood against the Ottomans at the Battle of Kosovo in 1389. The result was indecisive, but it led to the subsequent fall of Serbia. Stefan Lazarević, the son of Lazar, succeeded as ruler, but by 1394 he had become an Ottoman vassal. In 1402 he renounced Ottoman rule and became a Hungarian ally; the following years are characterized by a power struggle between the Ottomans and Hungary over the territory of Serbia. In 1453, the Ottomans 