Zadar was settled by the Illyrians in the 4th century BC. It was called Jader by the Romans, and later Diadora. It remained under Roman and Byzantine control until around the year 1000 when the Byzantines gave it to Venice. Venice competed for control of the port with the Hungarian kings, whose territory at that time extended to the Adriatic via Croatia.
At the end of the 12th century it was under Hungarian control, but was taken by the Venetians and the knights of the Fourth Crusade in 1202. The Crusaders had promised the Venetians a certain amount of money to pay for ships for transport to Egypt, and when they could not pay the Venetians diverted the Crusade to Zara. King Emeric of Hungary had declared that he would join the Crusade, and there was a controversy among the knights and clergy over whether or not a supposedly divine army could attack a fellow Christian. Many, including the elder Simon de Montfort, withdrew from the Crusade rather than attack the city. Nevertheless, Zara was taken, and Pope Innocent III excommunicated everyone involved (he later removed the excommunication from the Crusaders, but not from the Venetians). The city continued to pass between Venice and Hungary, until the Venetians finally bought the city from Hungary in 1409.
In 1797 it became part of Austria under the Treaty of Campo Formio, and from 1809 to 1813 it was part of Napoleon's empire. In 1815 it became the capital of Dalmatia, but was given to Italy by the Treaty of Saint-Germain after World War I. The Nazis occupied it in World War II, and after the war it became part of Croatia (at the time in Yugoslavia).