In 1430, Murad took charge of the attack on Thessalonika, now in the possession of the Venetians, who had taken it from the Greek prince Andronicus. The activity of Venice at this time is in decided contrast to the cautious policy displayed by the republic in the previous century. For one thing, the secular contest with Genoa had been decided in favor of the Adriatic port. Then, too, the objections of the Venetians to occupy continental possessions had been overcome by the exigencies of Italian politics, which had forced Venice to play a larger rôle in advancing her especial interests than ever before. It seemed for a time as if the Venetians would become the natural heirs to the territories of the Eastern Empire in the lands of peninsular Greece, while to the north Hungary had risen to be the main power, around which the Roumanian and Slavic races gathered as their natural protector against the Turk. From now on the establishment of the Ottoman power in Europe would depend on the overthrow of both the Venetians and the Hungarians. The former, as has just been intimated, were slowly and diplomatically acquiring Greek principalities in the south of continental Greece, but were striving, at the same time, not to bear the brunt of Turkish hostility. They relied partly on the strong fleet which had been sent to the East, and partly on the care they had taken to secure the aid of the Hungarians. On the other hand, the Turks had been developing their navy, and they ventured, as early as 1428, to attack merchant vessels belonging to the republic.
The fall of Thessalonika precipitated events and caused the Venetians to recognize that quick action was necessary. The republic entered into relations with the King of Cyprus and with the dissatisfied vassal princes of Karamania, who were ever ready to rebel against the Sultan. Proposals were made to King Sigismund to inaugurate a new crusade, in which he would have charge of the land forces, while the Venetians, keeping the mastery of the sea, would prevent new troops from being sent over from Asia. Unhappily, Sigismund proved apathetic; there were disturbances in the Albanian lands owned by Venice, and a war with Genoa kept the Venetians from having a free hand to deal effectively with the Sultan. Accordingly, a peace was patched up, by the terms of which Venice paid a tribute to the Turks for some of her Greek possessions.
Plundering expeditions were now made by the Turks into Hungarian territory, but before Sigismund could undertake military operations on his side his death occurred. (December 9, 1437.) The work of defense was then undertaken by his successor and son-in-law, Albert. For the first time the Sultan in person led an army in the region of the Carpathians and the Danube, and, although a coalition was formed, consisting of Hungarians, Servians, and Wallachians, the Turkish arms proved, as so often, irresistible. Semendria was taken, and many thousands of prisoners were carried away from the ravaged countries. But Belgrade held out, though Albert died there among his troops on October 27, 1438.
Strong hands were found ready to take up the work of defense. In the city, which was amply protected by a threefold wall, and by many pieces of artillery mounted on the ramparts, there was a garrison of German mercenaries, while in other regions exposed to the invaders, there were Hungarian forces under the command of Johann Hunyadi, the son of a Roumanian peasant of Inidora, whose reputation as a national hero was soon to be made in the victorious leadership of his people against the Turk.
Hunyadi’s first aggressive act was an invasion into Bosnia, where he drove out some marauding bands of the Turkish general Isa-beg. A much more important military exploit was the battle of Szt-Imre, where, in 1442 (March 18), the Turks were forced back into Wallachia. Attempts made somewhat later to avenge this humiliation had no final success, for Hunyadi attacked the invading army on its march, winning a victory conspicuous because many well-known Ottoman generals lost their lives.
Spurred by the prowess of Hunyadi, the Western powers prepared to support him in driving the Ottomans from Europe. There was additional ground for hope in the arrangements, lately made, for a union between the Eastern and Western churches, a scheme naturally regarded as a good basis for coöperation against the Moslems. A new crusade was proclaimed, but nothing was accomplished by it, since the Venetians feared the loss of their possessions in the East, if the Slavic races were too actively aided, and since the Pope had no inclination to part with the tithes collected for the crusade, while he had use for them in protecting his temporal sovereignty as an Italian prince.
The Hungarians, left for these sinister reasons to deal with the Turks single-handed, displayed no lack of resolution. Hunyadi, with troops of Roumanians and Hungarians, passed the Danube late in October, 1443. He soon occupied Nisch and defeated several Ottoman armies, but the campaign had no decisive result, for Hunyadi feared to penetrate farther into Turkish territory without additional forces, especially as Murad was now in personal command. This caution was justified, for, in withdrawing, the Christian army suffered a reverse. The Hungarians could congratulate themselves that their advance had given great encouragement wherever the pressure of the Turkish occupation was felt. Yet there was no sincere effort on the part of the Christian powers to work together. The Servians made their own terms with the Sultan, and the Venetian fleet, ostensibly despatched to eastern waters to act with the Hungarians, was put under the command of Loredano, who had private instructions to come to terms with the Turks.
The story of a peace concluded on terms most humiliating for Murad, by which, among other things, the whole of Bulgaria and Servia was evacuated, is rightly questioned. All that is known is that Wladislaw, who was now King of Hungary (1440), solemnly protested that he would undertake a crusade against the Turks, all treaties and truces to the contrary notwithstanding. The expedition was begun, Hunyadi coöperating, and Papal legates testifying, by their presence, that a true crusade was in progress. But, although the army stood for the cause of the whole of Christendom, in the ranks there were almost none but Hungarian soldiers. It crossed the Danube, intending to march straight to Varna, and from there proceed by sea to Constantinople. But it was far too small for the work it planned to do; even after it had been joined by Vlad of Wallachia, it only numbered 15,000 men. Before Varna could be taken, Murad (at the head of an army of 40,000 men) hastened from Asia to arrest the progress of the crusaders. In the engagement that followed all efforts to break through the Janitschars, even when attempted under the experienced leadership of Hunyadi, failed completely, and the Christians suffered a decisive overthrow. Only a few of the 15,000 escaped, among them Hunyadi and Vlad. Among the dead were the King of Hungary and a Papal legate. (October, 1444.)
The news of this disaster took some time to reach the West, and by the time it was known there, information was also received that the indefatigable Hunyadi was again girding himself up for a second expedition. This ended with some small advantages in Wallachia. Again, in 1448, he tried another mode of entrance into the Sultan’s territory, passing this time among the Albanians, on whose aid he reckoned without avail, since they were fighting on their own account against the Turks. The Servians, too, held aloof. The second battle of Kossovo (October 17, 1448) ended in a defeat for the Hungarians, although the Turkish losses were very severe. Under the hammering of Hunyadi, the Janitschars were obliged to give way, but they withdrew in good order with unbroken ranks.
There was a truce for three years after this battle, much to the relief of both sides, since Murad had encountered an aggressive Albanian leader in Scanderbeg, who seemed likely to rival Hunyadi as an enemy of Ottoman rule. For some time this Albanian champion, whose name in Albanian is equivalent to Alexander, had been kept as a page at the Sultan’s court. During the confusion caused by the campaigns of Hunyadi, the young man had managed to escape, but before doing so, he had forced the Sultan’s secretary, under menace of death, to sign an order directing the commander of Croia to give up the place to Scanderbeg. On reaching his home in the mountains, the Albanian chieftain put himself at the head of 600 warriors. Entering Croia alone he presented his written order to the governor, who immediately turned over the place to him. In the night he brought his men into the town and the Turkish garrison was massacred.