Following the capture of Krujë, Skanderbeg managed to bring together all the Albanian princes in the town of LezhëMinna Skafte Jensen, 2006, A Heroic Tale: Marin Barleti's Scanderbeg between orality and literacy (see League of Lezhë, 1444). Gibbon reports that "Albanians, a martial race, were unanimous to live and die with their hereditary prince" and that "in the assembly of the states of Epirus, Scanderbeg was elected general of the Turkish war and each of the allies engaged to furnish his respective proportion of men and money". With this support, Skanderbeg built fortresses and organized a mobile defense force that forced the Ottomans to disperse their troops, leaving them vulnerable to the hit-and-run tactics of the AlbaniansL.S. Stavrianos, 2000, The Balkans Since 1453, ISBN 1850655510. Skanderbeg fought a guerrilla war against the opposing armies by using the mountainous terrain to his advantage. Skanderbeg continued his resistance against the Ottoman forces until his death, with a force rarely exceeding 20,000.

Although it is commonly believed that Skanderbeg took part in the Second Battle of Kosovo in 1448, he actually never arrived. He and his army were en route to reinforce the mainly Hungarian army of John Hunyadi, but the Albanians were intercepted and defeated by Đurađ Branković of Serbia. Although Hunyadi was defeated in the campaign, Hungary successfully resisted and defeated the Ottoman campaigns during Hunyadi's lifetime.

In June 1450, an Ottoman army numbering approximately 150,000 men led by Sultan Murad II himself laid siege to Krujë. Leaving a protective garrison of 1,500 men under one of his most trusted lieutenants, Vrana Konti (also know as Kont Urani), Skanderbeg harassed the Ottoman camps around Krujë and attacked the supply caravans of the sultan's army. By September the Ottoman camp was in disarray as morale sank and disease ran rampant. Murad II acknowledged the castle of Krujë would not fall by strength of arms, and he lifted the siege and made his way to Edirne. Soon thereafter in the winter of 1450-51, Murad died in Edirne and was succeeded by his son Mehmed II.

For the next five years Albania was allowed some respite as the new sultan set out to conquer the last vestiges of the Byzantine Empire. The first real test between the armies of the new sultan and Skanderbeg came in 1455 during the Siege of Berat, and would end in the most disastrous defeat Skanderbeg would suffer. Skanderbeg had sieged the town's castle for months, causing the demoralized Turkish officer in charge of the castle to promise his surrender. At that point Skanderbeg relaxed the grip, split his forces and left the siege location. He left behind one of his generals and half of his cavalry at the bank of the river Osam to finalize the surrender. It would be a costly error.

The Ottomans saw this moment as an opportunity for attack. They sent a large cavalry force from Fushe in Kosovo to Berat as reinforcements. The Albanian forces had become overconfident and had been lulled into a false sense of security. The Ottomans caught the Albanian cavalry by surprise while they were resting in the shores of the Osam. Almost all the 5,000 Albanian cavalry laying siege to Berat were massacred. When Skanderbeg made it to the battlefield, everything was over; the Ottoman cavalry had already left for Anatolia. A reason of this defeat of Scanderbeg's army, was the betrayal of his nephew, Hamza Kastrioti who was an officer of Scanderbeg's cavalry that passed on the Ottoman side with other Albanian forces and gave the Ottomans important information about the locatin and the organization of the Albanian troops. Later Hamza Kastrioti was captured in the battlefield by Scanderbeg himself, and imprisoned in the castle of Krujë.

In 1457, an Ottoman army numbering approximately 80,000 men invaded Albania with the hope of destroying Albanian resistance once and for all; this army was led by Isa beg Evrenoz, one of the the only commanders to have defeated Skanderbeg in battle, and Hamza Kastrioti, Skanderbeg’s nephew. After wreaking much damage to the countryside, the Ottoman army set up camp at the Ujebardha field (literally translated as "Whitewater"), halfway between Lezhë and Krujë. After having evaded the enemy for months, Skanderbeg attacked there and defeated the Ottomans in September.

In 1461 the Sultan proposed terms of accommodation with Skanderbeg and a peace was concluded between them on June 22. In the same year, Skanderbeg launched a successful campaign against the Angevin noblemen and their allies who sought to destabilize King Ferdinand I of Naples. For his services he gained the title Duke of San Pietro in the kingdom of Naples. After securing the Neapolitan kingdom, a crucial ally in his struggle, he returned home. In 1464 Skanderbeg fought and defeated Ballaban Badera, an Albanian renegade who had captured a large number of Albanian army commanders John Musachi, 1515, Brief Chronicle on the Descendants of our Musachi Dynasty, including Moisi Arianit Golemi, a cavalry commander; Vladan Giurica, the chief army economist; Muzaka of Angelina, a nephew of Skanderbeg, and 18 other noblemen and army captains. These men, after they were captured, were sent immediately to Istanbul and tortured for fifteen days. Skanderbeg’s pleas to have these men back, by either ransom or prisoner exchange, failed.

In 1466 Sultan Mehmed II personally led an army into Albania and laid siege to Krujë as his father had attempted sixteen years earlier. The town was defended by a garrison of 4,400 men, led by Prince Tanush Topia. After several months, Mehmed, like Murad II, saw that seizing Krujë by force of arms was impossible for him to accomplish. Shamed, he left the siege to return to Istanbul. However, he left a force of 40,000 men under Ballaban Pasha to maintain the siege, even building a castle in central Albania, which he named El-basan (the modern Elbasan), to support the siege. Durrës would be the next target of the sultan, in order to be used as a strong base opposite the Italian coastFranz Babinger, 1992, Mehmed the Conqueror and His Time, ISBN 0691010781. The second siege of Kruja was eventually broken by Skanderbeg, resulting in the death of Ballaban Pasha from firearms.

A few months later in 1467, Mehmed, frustrated by his inability to subdue Albania, again led the largest army of its time into Albania. Krujë was besieged for a third time, but on a much grander scale. While a contingent kept the city and its forces pinned down, Ottoman armies came pouring in from Bosnia, Serbia, Macedonia, and Greece with the aim of keeping the whole country surrounded, thereby strangling Skanderbeg’s supply routes and limiting his mobility. During this conflict, Skanderbeg fell ill with malaria in the Venetian-controlled city of Lezhë, and died on January 17 1468, just as the army under the leadership of Leke Dukagjini defeated the Ottoman force in Shkodër.

Papal relations