The Ottoman Empire was founded by Osman I in 1299. His son, Orhan, captured its first capital, Bursa, from the Byzantine Empire. In the late 1300s, the Ottomans began consolidating power, especially in the Balkans, where Serbia was defeated in 1389 at the Battle of Kosovo Polje by Sultan Murad I. He died at the battle, and Bayezid I took control. At the 1396 Battle of Nicopolis, a large crusade of the Western European powers was defeated. Despite the victory, Bayezid was deposed by Tamerlane at the Battle of Ankara in 1402. His absence led to a civil war, referred to as the Ottoman Interregnum. Mehmed Çelebi won and became Mehmed I. His son, Murad II had to battle pretenders to the throne backed by the Byzantine Empire. He retaliated with an attack on Constantinople, and Venice helped the Byzantines. Murad defeated them at Thessaloniki. He also defeated the Karamanid "beylik" (principality), Hungary, Poland, and Wallachia at Varna in 1444. John Hunyadi, a Hungarian general, tried his hand at defeating the Turks but lost in 1448.