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War with Venice: 1447 to 1448

At the beginning of the Albanian insurrection, the Republic of Venice was supportive of Skanderbeg, considering his forces to be a buffer between them and the Ottoman Empire. Lezhë, where the eponymous league was established, was Venetian territory, and the assembly met with the approval of Venice. The later affirmation of Skanderbeg and his rise as a strong force on their borders, however, was seen as a menace to the interests of the Republic, leading to a worsening of relations and the dispute over the fortress of Dagnum which triggered the Albanian-Venetian War of 1447–48. After various attacks against Bar and Ulcinj, along with Đurađ Branković and Stefan Crnojević, and Albanians of the area, the Venetians offered rewards for his assassination. The Venetians sought to overthrow or assassinate Skanderbeg by any means, even offering a life pension of 100 golden ducats annually for the person who would kill him. During the conflict, Venice invited the Ottomans to attack Skanderbeg simultaneously from the east, facing the Albanians with a two-front conflict.

On 14 May 1448, an Ottoman army led by Sultan Murad II and his son Mehmed laid siege to the castle of Sfetigrad. The Albanian garrison in the castle resisted the frontal assaults of the Ottoman army, while Skanderbeg harassed the besieging forces with the remaining Albanian army under his personal command. On 23 July 1448, Skanderbeg won a battle near Shkodër against a Venetian army led by Andrea Venier. In late summer 1448, due to a lack of potable water, the Albanian garrison eventually surrendered the castle with the condition of safe passage through the Ottoman besieging forces, a condition which was accepted and respected by Sultan Murad II. Primary sources disagree about the reason why the besieged had problems with the water in the castle: While Barleti and Biemmi maintained that a dead dog was found in the castle well, and the garrison refused to drink the water since it might corrupt their soul, another primary source, an Ottoman chronicler, conjectured that the Ottoman forces found and cut the water sources of the castle. Recent historians mostly concur with the Ottoman chronicler's version. Although his loss of men was minimal, Skanderbeg lost the castle of Sfetigrad, which was an important stronghold that controlled the fields of Macedonia to the east. At the same time, he besieged the towns of Durazzo (modern Durrës) and Lezhë which were then under Venetian rule. In August 1448, Skanderbeg defeated Mustafa Pasha in Dibër at the battle of Oranik. Mustafa Pasha lost 3,000 men and was captured, along with twelve high officers. Skanderbeg learned from these officers that it was the Venetians who pushed the Ottomans to invade Albania. The Venetians, upon hearing of the defeat, urged to establish peace. Mustafa Pasha was soon ransomed for 25,000 ducats to the Ottomans.

On 23 July 1448, Skanderbeg crossed the Drin River with 10,000 men, meeting a Venetian force of 15,000 men under the command of Daniele Iurichi, governor of Scutari. Skanderbeg instructed his troops on what to expect and opened battle by ordering a force of archers to open fire on the Venetian line. The battle continued for hours until large groups of Venetian troops began to flee. Skanderbeg, seeing his fleeing adversaries, ordered a full-scale offensive, routing the entire Venetian army. The Republic's soldiers were chased right to the gates of Scutari, and Venetian prisoners were thereafter paraded outside the fortress. The Albanians managed to inflict 2,500 casualties on the Venetian force, capturing 1,000. Skanderbeg's army suffered 400 casualties, most on the right-wing. The peace treaty, negotiated by Georgius Pelino and signed between Skanderbeg and Venice on 4 October 1448, envisioned that Venice would keep Dagnum and its environs, but would cede to Skanderbeg the territory of Buzëgjarpri at the mouth of the river Drin, and also that Skanderbeg would enjoy the privilege of buying, tax-free, 200 horse-loads of salt annually from Durazzo. In addition, Venice would pay Skanderbeg 1,400 ducats. During the period of clashes with Venice, Skanderbeg intensified relations with Alfonso V of Aragon (r. 1416–1458), who was the main rival of Venice in the Adriatic, where his dreams for an empire were always opposed by the Venetians.

One of the reasons Skanderbeg agreed to sign the peace treaty with Venice was the advance of John Hunyadi 's army in Kosovo and his invitation for Skanderbeg to join the expedition against the sultan. However, the Albanian army under Skanderbeg did not participate in this battle as he was prevented from joining with Hunyadi's army. It is believed that he was delayed by Đurađ Branković, then allied with Sultan Murad II, although Brankovic's exact role is disputed. Skanderbeg was outraged at the fact that he had been prevented in participating in a battle which could have changed the fate of his homeland if not the entirety of the Balkan Peninsula. As a result of this he let his armies raid into Kosovo, he then set fire to Serbian villages and slaughtered their inhabitants to punish Brankovic. He then returned to Krujë towards the end of November. Antonio Bonfini an Italian courtier of the Hungarian king believed the battle could been won if Skanderbeg had participated. He appears to have marched to join Hunyadi immediately after making peace with the Venetians, and to have been only 20 miles from Kosovo Polje when the Hungarian army finally broke.