Siege of Belgrade
Faced with the overwhelming force of the Ottoman Empire, the nobility of the Kingdom of Croatia was alarmed as the Siege of Belgrade of 1521 caused the Kingdom of Hungary to lose its last fortress on the Danube to Suleiman the Magnificent. King Louis II showed no interest in defense, and was in a dire financial situation at the time. The Croatians appealed to the Pope, Venice, Emperor Charles V and Archduke Ferdinand for help, but had little success.