Battle of Varna
Murad II then declared war against Venice, the Karamanid Emirate, Serbia and Hungary. The Karamanids were defeated in 1428 and Venice withdrew in 1432 following the defeat at the second Siege of Thessalonica in 1430. In the 1430s Murad captured vast territories in the Balkans and succeeded in annexing Serbia in 1439. In 1441 the Holy Roman Empire and Poland joined the Serbian-Hungarian coalition. Murad II won the Battle of Varna in 1444 against John Hunyadi.