After the Battle of Kosovo in 1389, the Ottomans had conquered most of the Balkans and had reduced the Byzantine Empire to the area immediately surrounding Constantinople, which they blockaded from 1394 on. In the eyes of the Bulgarian boyars, despots, and other independent Balkan rulers, the crusade was a great chance to reverse the course of the Ottoman conquest and take back the Balkans from Islamic rule. In addition, the front line between Islam and Christianity had been moving slowly towards the Kingdom of Hungary. The Kingdom of Hungary was now the frontier between the two religions in Eastern Europe, and the Hungarians were in danger of being attacked themselves.

The Republic of Venice feared that Ottoman control of the Balkan peninsula, which included Venetian territories like parts of Morea and Dalmatia, would reduce their influence over the Adriatic Sea, Ionian Sea, and Aegean Sea. In 1394, Pope Boniface IX proclaimed a new crusade against the Turks, although the Western Schism had split the papacy in two, with rival popes at Avignon and Rome, and the days when a pope had the authority to call a crusade were long past. Venice supplied a naval fleet for supporting action, while Hungarian envoys encouraged German princes of the Rhineland, Bavaria, Saxony, and other parts of the empire to join.

The Battle of Nicopolis resulted in the rout of the allied crusader army of Hungarian, Croatian, Bulgarian, Wallachian, French, Burgundian, German, and assorted troops (assisted by the Venetian navy) at the hands of an Ottoman force, leading to the end of the Second Bulgarian Empire.