The war was sparked by Villehardouin's intervention in a succession dispute over the northern third of the island of Euboea, which was resisted by the local Lombard barons (the "triarchs") with the aid of the Republic of Venice.

William of Villehardouin, who in 1246 had succeeded his elder brother as prince, was a most energetic ruler, who aimed to expand and consolidate his rule over the other Latin states.

[2] Guy I de la Roche, the "Great Lord" of Athens and Thebes, was already his vassal for the fief of Argos and Nauplia, which lay in the Peloponnese,[3] and William was also suzerain of the three Lombard baronies (terzieri, lit.

Already in 1209, when all of Euboea was still under the rule of Ravano dalle Carceri, it had been granted trade privileges and the right to establish quarters in every town of the island, while the lord of Euboa pledged to send each year a tribute and a rich garment to the Doge of Venice as token of its suzerainty.

[7] Carintana is commonly considered by modern historians to have been the second wife of William of Villehardouin,[8][6] based on the work by the 19th-century scholar Karl Hopf, but this has been proven as erroneous by Raymond-Joseph Loenertz.

The previous agreements of 1209 and 1216 were renewed, but, while the triarchs and their domains were freed from any duties and the considerable tribute that they paid to Venice until then, they in turn gave up the rights to all customs revenue to the Republic.

[16][15][19] More importantly, the triarchs ceded to the Republic full possession of the strategic citadel that guarded the bridge over the Euripus Strait, and of extensive properties in the city of Negroponte itself.

Othon de Cicon, the lord of Karystos in southern Euboea, in control of the strategic passage of the Cavo D'Oro, also sided with Villehardouin.

[16][24][18] Villehardouin responded by sending his nephew, the baron of Karytaina, Geoffrey of Briel, who recaptured the city of Negroponte and launched devastating raids in Euboea.

Guy de la Roche presented himself before it accompanied by his own knights, but the assembled barons decided that they did not have the authority to judge him, and referred the matter to King Louis IX of France (r. 1226–1270).

[28] The renegade Geoffrey of Briel too was brought for judgement before William, and it was only the determined and passionate intercession of the other barons that saved his life and secured a pardon from the vengeful prince.

[29] William's victory at Karydi, coupled with a victory of his troops against the Venetians near Oreos, brought an effective end to the conflict; on 6 August 1258, Guglielmo da Verona and Narzotto dalle Carceri consented to begin negotiations for peace through the Doge of Venice, and in early 1259, the Doge authorized the new bailo, Andrea Barozzi, to sign a treaty with William.