After the fall of Constantinople to the Ottoman Empire in 1453, Mehmed set his sights on other campaigns. In Anatolia, the Greek Empire of Trebizond was still resisting the Ottomans, and to the East the White Sheep Turkomans of Uzun Hasan, together with other smaller states, threatened the Ottomans. In the West, Skanderbeg in Albania continued to trouble the Sultan, while Bosnia was sometimes reluctant in paying the jizya. Wallachia controlled the left bank of the Danube, and Mehmed wanted to have control over the river, as naval attacks could be launched against his empire all the way from the Holy Roman Empire. On September 26, 1459, Pope Pius II called for a new crusade against the Ottomans and on January 14, 1460, at the Congress of Mantua, the Pope proclaimed the official crusade that was to last for three years. His plan, however, failed and the only European leader that showed enthusiasm for the crusade was Vlad Țepeș, whom the Pope held in high regard.[6] Because of a lack of enthusiasm shown by Europeans for the crusade, Mehmed took the opportunity to take an offensive stand. Later that same year (1460), he captured the last independent Serbian city, Smederevo, and in 1461, he convinced the Greek despot of Morea to give up his stronghold; soon thereafter, its capital, Mistra, and Corinth followed suit and surrendered themselves without struggle.[7]
Vlad Țepeș's only ally, Mihály Szilágyi, was captured in 1460 by the Turks while traversing Bulgaria. Szilágyi's men were tortured to death, while Szilágyi was sawed in half.[7] Later that year, Mehmed sent envoys to Vlad to urge him to pay the delayed jizya. Vlad Țepeș provoked Mehmed by having the envoys killed and in a letter dated September 10, 1460, addressed to the Transylvanian Saxons of Kronstadt (today: Brașov), he warned them of Mehmed's invasion plans and asked for their support.[8] Vlad Țepeș had not paid the annual jizya of 10,000 ducats since 1459. In addition to this, Mehmed asked him for 1,000 boys that were to be trained as janissaries. Vlad Țepeș refused the demand, and the Turks crossed the Danube and started to do their own recruiting, to which Vlad reacted by capturing the Turks and impaling them.[9] The conflict continued until 1461, when Mehmed asked the Prince to come to Constantinople and negotiate with him.
At the end of November 1461, Vlad Țepeș wrote to Mehmed that he could not afford to pay the jizya, as his war against the Saxons of Transylvania had emptied his resources, and that he could not leave Wallachia and risk having the Hungarian king take over his domains. He further promised to send the Sultan plenty of gold when he could afford to and that he would go to Constantinople if the Sultan would send him a pasha to rule over Wallachia in his absence.[10] Meanwhile, the Sultan received intelligence reports that revealed Vlad's alliance with Hungarian king, Matthias Corvinus. He sent the bey of Nicopolis, Hamza Pasha, to stage a diplomatic meeting with Vlad at Giurgiu, but with orders to ambush him there; and thereafter, take him to Constantinople.[11] Vlad was forewarned about the ambush and planned to set an ambush of his own. Hamza brought with him 1,000 cavalry and when passing through a narrow pass north of Giurgiu, Vlad launched a surprise-attack. The Wallachians had the Turks surrounded and fired with their handgunners until the entire expedition-force was killed. Historians credit Vlad Țepeș as one of the first European crusaders to use gunpowder in a "deadly artistic way".[12] In a letter to Corvinus, dated February 11, 1462, he wrote that Hamza Pasha was captured close to the former Wallachian fortress of Giurgiu. He then disguised himself as a Turk and advanced with his cavalry towards the fortress where he ordered the guards in Turkish to have the gates open.[11] This they did and Vlad Țepeș attacked and destroyed the fortress.[11] In his next move, he went on a campaign and slaughtered enemy soldiers and population that might have sympathized with the Turks; first in southern Wallachia, then, in Bulgaria by crossing the frozen Danube. While in Bulgaria, he divided his army into several smaller groups and covered "some 800 kilometers in two weeks", as they killed over 23,000 Turks. In a letter to Corvinus, dated February 11, 1462, he stated:[13]
I have killed peasants men and women, old and young, who lived at Oblucitza and Novoselo, where the Danube flows into the sea, up to Rahova, which is located near Chilia, from the lower Danube up to such places as Samovit and Ghighen. We killed 23,884 Turks without counting those whom we burned in homes or the Turks whose heads were cut by our soldiers...Thus, your highness, you must know that I have broken the peace with him (Sultan Mehmet II).
The Christian Bulgarians were spared and many of them were settled in Wallachia.