The defeat at Ankara in 1402 was the first real setback for the Ottoman empire. Its sultan - Bayezid became a hostage of the new conqueror Timur, and soon sons of the sultan started fighting each other in order to get to the throne. This period is called Ottoman Interregnum, but it was basically a Civil War between 6 princes. Eventually, this civil war came to an end, and as the agressive invasion of the South and Central Europe continued, Hungary, Poland, Serbia, Bosnia, Croatia, Bulgaria, Transylvania, Lithuania, Wallachia, Bohemia, Ruthenia and others started a crusade called the Crusade of Varna against the Ottoman sultan Murad II. The crusade was concluded in 1444 with the battle of Varna between Murad II on one side, king of Poland and Hungary Wladyslaw III and voivode of Transylvania John Hunyadi on the other.