Which crusade was diverted to attack the Christian city of Zara in 1202?

The Fourth Crusade was diverted to attack the Christian city of Zara, now Zadar, in 1202. Zara was controlled by the Kingdom of Hungary and Croatia and had long been contested by Hungary and Venice, whose commercial interests dominated the Adriatic.

The crusaders had contracted with Venice to provide ships and transport for the expedition, but they could not pay the full agreed cost. Venice's doge, Enrico Dandolo, proposed that the crusaders capture Zara in return for help settling Venice's dispute with the city. The diversion changed the character of the campaign before it even reached the eastern Mediterranean.

The siege began on 10 November 1202 and Zara fell on 24 November. The city was Catholic, making the attack especially controversial: Pope Innocent III had explicitly forbidden it and threatened participants with excommunication. Some crusaders, including Simon de Montfort, refused to take part.

After spending the winter at Zara, the crusaders accepted another diversion and went on to Constantinople. In 1204 they captured and sacked the Byzantine capital, an outcome that permanently deepened the division between Western and Eastern Christianity. The attack on Zara is therefore a defining episode of the Fourth Crusade, not the Fifth or Sixth.