The Uprising of Konstantin and Fruzhin

The uprising of Konstantin and Fruzhin, beginning in 1404 or 1408, was a military campaign against Ottoman domination in the eastern Balkans. Information about this episode is scarce and has prompted differing interpretations among historians. Although the course of events and the precise dates of its beginning and end remain unclear, the uprising is known to have involved Serbs, Hungarians and Wallachians united against the Ottomans.
In 1403–1404, the rulers of Hungary, Serbia, Bosnia and Wallachia formed a military alliance led by Sigismund I, the future emperor. The Bulgarian rulers Konstantin II Asen and Fruzhin, son of Tsar Ivan Shishman, joined the alliance. In 1408, exploiting the Ottoman Empire's internal crisis, they liberated Vidin from Turkish rule. With support from the Wallachian voivode Mircea the Elder, the Bosnian king Ostoja and the Hungarian ruler Sigismund, the uprising spread into the Timok and Pirot regions, becoming the first uprising against Ottoman rule on the Balkan Peninsula.
 

Although initially successful, the uprising suffered a setback in 1409 when Bayezid's son Süleyman drove the rebel forces towards the Morava Valley and defeated them. According to some sources, the uprising continued until 1413, when it was suppressed near the Temska River.