The failure of the Pazzi Conspiracy against Florence in 1478 and the unexpected peace as a result of Lorenzo de' Medici's daring personal diplomacy with Ferdinand I of Naples, the Pope's erstwhile champion, is a source of discontent among the Venetians and Pope Sixtus IV alike.

Venice, having ended its long conflict with the Ottoman Turks in 1479 with the Treaty of Constantinople, is thus free to turn its complete attention to its role in its terra firma (main land) and generally to the peninsula of Italy.

In addition to the usual minor friction over strongholds along the borders, there is a contest over the commerce in salt, which is reserved to Venice by a commercial pact.

Nevertheless, Ferrara, which is ruled by Ercole I d'Este, has begun to take control over the saltworks at Comacchio.

This appears to be a threat to mainland interests of the Serenissima.

Venice is supported by Girolamo Riario, lord of Imola and Forlì,—the nephew of Pope Sixtus—who had taken possession of the strategic stronghold of Forlì in September 1480, with quick papal confirmation, and who now looks towards Ferrara in extending Della Rovere territory.

The immediate casus belli at the beginning of 1482 is a minor infraction of prerogatives: Venice had maintained a representative in Ferrara with the high title of visdominio, under whose care was the Venetian community in Este lands.

The visdominio, overreaching his mandate in 1481 with the arrest of a priest for debt, had been excommunicated by the vicar of the bishop of Ferrara, and forced out of the city.

On this excuse, war is declared.

Allied with Venice, besides the papal troops and Riario, are contingents supplied by the Republic of Genoa and William VIII, Marquis of Montferrat.