Ottoman Empire
The Ottoman Empire was founded by Osman I in 1299. His son, Orhan, fought against the Byzantine Empire and captured the city of Bursa in 1324. In the late 1300s, the Ottomans began consolidating power in the Balkans. Sultan Murad I defeated Serbia in 1389 at the Battle of Kosovo. He died at the battle, and his son Bayezid I took control. At the 1396 Battle of Nicopolis, he defeated a large crusade of the Christian kingdoms. But Bayezid was deposed by Tamerlane at the Battle of Ankara in 1402. His absence led to a civil war, which is known as the Fetret period (Ottoman Interregnum). Mehmed Çelebi defeated his brothers and acquired the throne. His son, Murad II, besieged Constantinople, but was unsuccessful because of a rebellion in Anatolia. He won a war against the Karamanids in 1423 and also against a large Christian alliance of Hungary, Poland, and Wallachia at the Battle of Varna in 1444. John Hunyadi, a Hungarian general, tried defeating the Ottomans but lost at the Second Battle of Kosovo in 1448.