Since the capture of Belgrad by the Turks in 1521, hostilities on the Hungarian frontier had never ceased, and the Turkish danger had been constantly before the Reichstag and in the mind of the Pope. In April, 1526, Suleiman started with a large army for his first regular Hungarian campaign. The Hungarian nobles, continually at feud with one another, were utterly unprepared to resist him, and the treasury was exhausted. The first city to be taken was Peterwardein, which was stormed by Ibrahim Pasha. Then fell Illok and Esek. But the decisive victory of the campaign was the battle of Mohacz, August 29, 1526. In this brief but bloody conflict little King Lewis fell, and the country was laid open to the sultan. The keys of Buda, the capital of Hungary, were handed over to him and he entered the city on September 1st. In spite of the express prohibition of the sultan, his soldiers accustomed to regard war as an opportunity for rapine, burned two quarters of the city, including the great church, while the akinji (scouts) burned neighboring villages and slaughtered the peasants. Other victories followed until at last the sultan, promising the Hungarians that John Zapolya should be their king, withdrew his army to Constantinople, carrying with him an immense amount of booty. The death at Mohacz of King Lewis without direct heirs left the thrones of Hungary and Bohemia vacant. The Archduke Ferdinand, as the husband of Lewis’ sister, and recognized as Lewis’ successor by official acts of his brother, the Emperor Charles, passed at the Diets of Worms and Brussels on April 28, 1521, and March 18, 1522, was the legal heir to the throne. But the sovereignty was claimed also by John Zapolya, voivode of Transylvania, a vigorous fighter and an unscrupulous politician. Both of these claimants had themselves been recognized in Hungary and crowned with the Iron Crown,[102] and both of them turned for substantial aid in support of their claims to Suleiman, regardless of possible loss of independence. Suleiman, as conqueror of the strongholds of Hungary, and as a court of appeal for the rivals, considered himself to have in his hand the disposition of the crown. He did not want it himself. He had expressly declared that he invaded Hungary to avenge insults, not to take the kingdom from Lewis; but the death of the latter forced him to choose between the two rival claimants. His word had been pledged for the support of Zapolya, and his dislike of the Hapsburgs and his friendship for the French king inclined him to keep it.