In 1428, while the Ottoman Empire was fighting a war with the Republic of Venice and the Kingdom of Hungary they achieved a temporary peace by establishing the Serbian Despotate as a buffer state. After the war ended in 1430, the Ottomans returned to their earlier objective of controlling all lands south of the Danube. In 1432, Sultan Murad II began raiding into Transylvania. After King Sigismund died in 1437, the attacks intensified, with the Ottomans occupying Borač in 1438 and Zvornik and Srebrenica in 1439. At the end of 1439, Smederevo capitulated and Murad succeeded in making Serbia an Ottoman province. Đurađ Branković, Despot of Serbia, fled to his estates in Hungary. In 1440, Murad besieged Hungary's main border fortress, Belgrade. After failing to take the fortress, he was forced to return to Anatolia to stop attacks by the Karamanids.

Meanwhile, Sigismund's successor Albert had died in October 1439, shortly after signing a law to "restore the ancient laws and customs of the realm". The law restricted the royal authority by requiring the participation of landed nobility in political decisions. Four months after Albert's death, his only son, Ladislaus, was born while Hungary was in the midst of a civil war over the next monarch. On 17 July 1440 Vladislaus, king of Poland, was crowned despite continuing disputes. John Hunyadi aided Vladislaus's cause by pacifying the eastern counties, gaining him the position of Nádor of Transylvania and the corresponding responsibility of protecting Hungary's southern border. By the end of 1442, Vladislaus had secured his status in Hungary, and rejected an Ottoman proposal of peace in exchange for Belgrade.

The Roman Catholic Church had long been advocating for a crusade against the Ottomans, and with the end of both the Hungarian civil war and a nearly simultaneous one in Byzantium, they were able to begin negotiations and planning realistically. The impetus required to turn the plans into action was provided by Hunyadi between 1441-42. In 1441, he defeated a raid led by Ishak Pasha of Smederevo. He nearly annihilated Mezid Bey's army in Transylvania on 22 March 1442, and in September he defeated the revenge attack of Şihabeddin Pasha, governor-general of Rumelia. Branković, hoping to liberate Serbia, also lent his support after Novo Brdo, the last major Serbian city, fell to the Ottomans in 1441.

Early fighting

On 1 January 1443 Pope Eugene IV published a crusading bull. In early May, it was reported "that the Turks were in a bad state and that it would be easy to expel them from Europe". War was proclaimed against Sultan Murad II at the diet of Buda on Palm Sunday 1443, and with an army of 40,000 men, mostly Magyars, the young monarch, with Hunyadi commanding under him, crossed the Danube and took Nish and Sofia.

The crusaders, led by Vladislaus, Hunyadi, and Branković, attacked in mid-October. They correctly expected that Murad would not be able quickly to mobilize his army, which consisted mainly of fief-holding cavalrymen (timariots) who needed to collect the harvest to pay taxes. Hunyadi's experience of winter campaigns from 1441-42 added to the Hungarians' advantage. They also had better armor, often rendering the Ottoman weapons useless. Murad could not rely on the loyalty of his troops from Rumelia, and had difficulties countering Hungarian tactics.

Battle of Nish

In the Battle of Nish the crusaders were victorious and forced Kasim Pasha of Rumelia and his co-commander Turahan Bey to flee to Sofia, Bulgaria to warn Murad of the invasion. However, the two burned all the villages in their path in an attempt to wear down the crusaders with a scorched earth tactic. When they arrived in Sofia, they advised the Sultan to burn the city and retreat to the mountain passes beyond, where the Ottoman's smaller army would not be such a disadvantage.

Battle of Zlatitsa

Shortly after, bitter cold set in, and the next encounter, fought at Zlatitsa Pass on 12 December 1443, was fought in the snow. Until the Battle of Zlatitsa the crusaders did not meet a major Ottoman army, but only town garrisons along their route toward Adrianople. Finally, at Zlatitsa they met strong and well positioned defence forces of the Ottoman army. The crusaders were defeated. As they marched home, however, they ambushed and defeated a pursuing force in the Battle of Kunovica, where Mahmud Bey, son-in-law of the Sultan and brother of the Grand Vizier Çandarlı Halil Pasha, was taken prisoner. Four days after this battle the Christian coalition reached Prokuplje. Đurađ Branković proposed to Władysław III of Poland and John Hunyadi that they stay in Serbian fortified towns during the winter and continue their campaign against the Ottomans in Spring 1444. They rejected his proposal, and retreated. By the end of January 1444 forces of Władysław and Hunyadi reached Belgrade, and in February they arrived at Buda where they were greeted as heroes.

While the battle at Zlatitsa Pass had been a defeat, the ambush returned to the crusaders the impression of an overall Christian victory, and they returned triumphant. The King and Church were both anxious to maintain this impression, and gave instructions to spread word of the victories, but contradict anyone who mentioned the loss.

Murad, meanwhile, returned angry and dejected by the unreliability of his forces, and imprisoned Turahan after blaming him for the army's setbacks and Mahmud Bey's capture.

Peace proposals

Murad is believed to have had the greatest wish for peace. Among other things, his sister begged him to obtain her husband Mahmud's release, and his wife Mara, daughter of Đurađ Branković, added additional pressure. On 6 March 1444 Mara sent an envoy to Branković; their discussion started the peace negotiations with the Ottoman Empire.

On 24 April 1444 Vladislaus sent a letter to Murad, stating that his ambassador, Stojka Gisdanić, was travelling to Edirne with full powers to negotiate on his behalf. He asked that, once an agreement was reached, Murad sent his own ambassadors with the treaty and his sworn oath to Hungary, at which point Vladislaus could also swear.

That same day, Vladislaus held a Diet at Buda, where he swore before Cardinal Julian Cesarini to lead a new expedition against the Ottomans in the summer. The strongest remaining supporter of Ladislaus' claim for the throne also agreed to a truce, thus removing the danger of another civil war.

Between June and August 1444, negotiations for a treaty were carried out, first in Edirne, and then in Szeged. The crusaders were not entirely interested in peace, however, especially with Cesarini pushing for the crusade's continuation. The Cardinal eventually found a solution that would allow for both the continuation of fighting and the ratification of the treaty, and on 15 August 1444 the Peace of Szeged was sworn into effect.

Final stage

Shortly after all the short-term requirements of the treaty were fulfilled, the Hungarians and their allies resumed the crusade. Murad, who had retired shortly after the treaty was completed, was called back to lead the Ottoman army. On 10 November 1444 the two armies clashed at the Battle of Varna (near the Black Sea fortress of Varna, Bulgaria). The Ottomans won a decisive victory despite heavy losses, while the crusaders lost their king and over 15,000 men.

Many of the Crusaders were crippled by frostbite, many more died in smaller follow-up battles, and many Europeans were captured. Hungary fell back into civil war until Hunyadi was elected Regent for the infant Ladislaus in June 1446. Branković retained control over Serbia.

The Ottoman victory in Varna, followed by their victory in the Second Battle of Kosovo in 1448, deterred the European states from sending substantial military assistance to the Byzantines during the Ottoman conquest of Constantinople in 1453. Although Pius II officially declared a three-year crusade at the Council of Mantua to recapture Constantinople from the Ottomans, the leaders who promised 80,000 soldiers to it reneged on their commitment. The Ottoman Empire was free, for several decades, from any further serious attempts to push it out of Europe.

The mixed Papal army was composed mainly of Hungarian, Polish, Bohemian (whose combined armies numbered 16,000) and Wallachian (7,000) forces, with smaller detachments of Czechs, Papal knights, Teutonic Knights, Bosnians, Croatians, Bulgarians, Lithuanians and Ruthenians.

Papal, Venetian and Genoese ships under Alvise Loredan had blockaded the Dardanelles as the Hungarian army was to advance on Varna, where it would meet the Papal fleet and sail down the coast to Constantinople, pushing the Ottomans out of Europe. The Hungarian advance was rapid, Ottoman fortresses were bypassed, while local Bulgarians from Vidin, Oryahovo, and Nicopolis joined the army (Fruzhin, son of Ivan Shishman, also participated in the campaign with his own guard). On October 10 near Nicopolis, some 7,000 Wallachian cavalrymen under Mircea II, one of Vlad Dracul's sons, also joined.

Armenian refugees in the Kingdom of Hungary also took part in the wars of their new country against the Ottomans as early as the battle of Varna in 1444, when some Armenians were seen amongst the Christian forces.

Late on November 9, a large Ottoman army of around 60,000 men approached Varna from the west. At a supreme military council called by Hunyadi during the night, the Papal legate, cardinal Julian Cesarini, insisted on a quick withdrawal. However, the Christians were caught between the Black Sea, Lake Varna, the steep wooded slopes of the Franga Plateau (356 m high), and the enemy. Cesarini then proposed a defense using the Wagenburg of the Hussites until the arrival of the Christian fleet. The Hungarian magnates and the Croatian and Czech commanders backed him, but the young (20-year-old) Władysław and Hunyadi rejected the defensive tactics. Hunyadi declared: "To escape is impossible, to surrender is unthinkable. Let us fight with bravery and honor our arms." Władysław accepted this position and gave him the command. Andreas del Palatio states that Hunyadi commanded the "Wallachian army" indicating a large Romanian component in Hunyadi's personal army.

In the morning of November 10, Hunyadi deployed the army of some 20,000 crusaders as an arc between Lake Varna and the Franga plateau; the line was about 3.5 km long. Two banners with a total of 3,500 men from the king's Polish and Hungarian bodyguards, Hungarian royal mercenaries, and banners of Hungarian nobles held the center. The Wallachian cavalry was left in reserve behind the center.

The right flank that lined up the hill towards the village of Kamenar numbered 6,500 men in 5 banners. Bishop Jan Dominek of Varadin with his personal banner led the force; Cesarini commanded a banner of German mercenaries and a Bosnian one. The Bishop of Eger led his own banner, and the military governor of Slavonia, ban Franco Talotsi, commanded one Croatian banner.

The left flank, a total of 5,000 men in 5 banners, was led by Michael Szilágyi, Hunyadi's brother in law, and was made up of Hunyadi's Transylvanians, Bulgarians, German mercenaries and banners of Hungarian magnates. Behind the Hungarians, closer to the Black Sea and the lake, was the Wagenburg, defended by 300 or 600 Czech and Ruthenian mercenaries under hetman Ceyka, along with Poles, Lithuanians and Wallachians. Every wagon was manned by 7 to 10 soldiers and the Wagenburg was equipped with bombards.

The Ottoman center included the Janissaries and levies from Rumelia deployed around two Thracian burial mounds. Murad observed and directed the battle from one of them. The Janissaries dug in behind ditches and two palisades. The right wing consisted of Kapikulus and Sipahis from Rumelia, and the left wing was made up by Akıncıs, Sipahis from Anatolia, and other forces. Janissary archers and Akıncı light cavalry were deployed on the Franga plateau.

Movements of the forces during the battle..

The light Ottoman cavalry assaulted the Croats of ban Franco Talotsi. Christians from the left riposted with bombards and firearms and stopped the attack. Christian soldiers chased the Ottomans in a disorderly pursuit. The Anatolian cavalry ambushed them from the flank. The Christian right wing attempted to flee to the small fortress of Galata on the other side of Varna Bay, but most of them were slain in the marshland around Varna Lake and the River Devnya, where Cesarini also met his end. Only ban Talotsi's troops managed to withdraw behind the Wagenburg.

The other Ottoman flank assaulted the Hungarians and Bulgarians of Michael Szilagyi. Their push was stopped and turned back; then Sipahis attacked again. Hunyadi decided to help and advised Władysław to wait until he returned; then advanced with two cavalry companies. The young king, ignoring Hunyadi's advice, rushed 500 of his Polish knights against the Ottoman center. They attempted to overrun the Janissary infantry and take Murad prisoner, and almost succeeded, but in front of Murad's tent Władysław's horse either fell into a trap or was stabbed, and the king was slain by mercenary Kodja Hazar, who beheaded him while doing so. The remaining coalition cavalry were demoralized and defeated by the Ottomans.

On his return, Hunyadi tried frantically to salvage the king's body, but all he could accomplish was to organize the retreat of the remains of his army; it suffered thousands of casualties in the chaos, and was virtually annihilated. Neither the head nor body of the king have ever been found. The minnesinger Michael Beheim wrote a song based on the story of Hans Mergest who spent 16 years in Ottoman captivity after the battle.

The death of Władysław left Hungary in the hands of the four-year-old Ladislaus Posthumous of Bohemia and Hungary. He was succeeded in Poland by Casimir IV Jagiellon after a three-year interregnum.

Murad's casualties at Varna were so heavy, it was not until three days later that he realized he was victorious. Nevertheless, the Ottoman victory in Varna, followed by the Ottoman victory in the Second Battle of Kosovo in 1448, deterred the European states from sending any substantial military assistance to the Byzantines during the Ottoman siege of Constantinople in 1453.

Hungarian King Vladislaus I leading the cavalry charge that would get him killed at Varna, by 19th century Polish painter Jan Matejko.

In the aftermath, the Ottomans had removed a significant opposition to their expansion into central and eastern Europe; subsequent battles forced a large number of Europeans to become Ottoman subjects.

The fallen Polish King was named Władysław III Warneńczyk in memory of the battle.

The Battle of Varna is commemorated on the Tomb of the Unknown Soldier, Warsaw, with the inscription "WARNA 10 XI 1444".

Chalkokondyles was a member of a prominent family of Athens, which at the time was ruled by the Florentine Acciaioli family. His father George was a kinsman of Maria Melissene, the wife of Duke Antonio I Acciaioli. When Antonio died in 1435, Maria attempted to secure control of the Duchy of Athens and sent George on a mission to the Ottoman Sultan Murad II, asking that the government of Athens might be entrusted to herself and George Chalkokondyles. However, during his absence, the Duchess was enticed out of the Acropolis and a young scion of the Acciaiuoli family, Nerio II, was proclaimed Duke of Athens. Meanwhile, George Chalkokondyles had his proposal rejected, despite offering the Sultan 30,000 gold pieces, and was cast into prison. George Chalkokondyles managed to escape to Constantinople, according to William Miller "leaving his retinue, tents and beasts of burden behind him", but after leaving Constantinople by ship, he was captured by an Athenian ship and taken back to the Sultan, who pardoned him.

George with Laonikos and the rest of the family relocated to the Peloponnese, which was under Byzantine rule as the Despotate of the Morea. In 1446 Constantine Palaiologos, then Despot of the Morea, sent George on a diplomatic mission to Murad II to obtain the independence of the Greek states south of Thermopylae; enraged at the offered terms, the Sultan put George Chalkokondyles into prison, then marched on Constantine's forces holding the Hexamilion wall on the Isthmus of Corinth and after bombarding it for three days, destroyed the fortifications, massacred the defenders, then pillaged the countryside, ending all hopes of independence. According to Miller, Laonikos was "evidently" an eye-witness to this battle, although the historian Theodore Spandounes claims Laonikos was the secretary of Murad II and present at the Battle of Varna in 1444.

The one glimpse we have of Laonikos himself is in the summer of 1447, when Cyriacus of Ancona met him in the summer of 1447 at the court of Constantine Palaiologos at Mistra. Cyriacus describes him as a youth egregie latinis atque grecis litteris eruditum ("surprisingly learned in Latin and Greek literature"). It was at Mistra where Laonikos was taught by George Gemistos Plethon, and who gave Laonikos his personal copy of the Histories of Herodotus: Laur. Plut. 70.6, written in 1318, with corrections by Plethon, and later used by Bessarion in 1436 to make another copy, contains a subscription written by Laonikos.

Laonikos' movements and actions after 1447 are not known with certainty. Internal evidence has led Byzantinist Anthony Kaldellis to put the date Laonikos stopped writing his Histories as 1464. In writing this work, his account of the circumcision of Sultan Mehmed II's sons in 1457 suggest he was an eye-witness to the event, and his account of Ottoman finances indicate he interviewed the Sultan’s accountants. Other speculations about Laonikos Chalkokondyles' life are not as widely accepted.

After the Fall of Constantinople, Chalkokondyles wrote his most important historical work, Proofs of Histories (Ἀποδείξεις Ἱστοριῶν). This historical work comprises one of the most important sources for the students of the final 150 years of Byzantine history, despite being defective in its chronology. It covers the period from 1298-1463, describing the fall of the Byzantine empire and the rise of the Ottoman Turks, which forms the centre of the narrative, down to the conquest of the Venetians and Mathias, king of Hungary, by Mehmed II. The capture of Constantinople he rightly regarded as an historical event of far-reaching importance and compared it to the fall of Troy. The work also sketches other manners and civilization of England, France and Germany, whose assistance the Greeks sought to obtain against the Turks. For his account of earlier events he was able to obtain information from his father.

His model is Thucydides (according to Bekker, Herodotus), his language is tolerably pure and correct, and his style is simple and clear. The text, however, is in a very corrupt state. The archaic language he used made his texts hard to read in many parts, while the antiquarian names, with which he named people of his time, created confusion (Γέται, Δάκες, Λίγυρες, Μυσο, , Παίονες, Ἕλληνες), The extended use of the name “Hellenes” (Ἕλληνες), which Laonikos used to describe the Byzantines contributed to the connection made between the ancient Greek civilization and the modern one.

Chalkokondyles' History was first published in a Latin translation by Conrad Clauser at Basel in 1556, although the translation itself bears the date of November 1544. A French translation was published by Blaise de Vigenère in 1577 with a later edition by Artus Thomas, with valuable illustrations on Turkish matters. The editio princeps of the Greek text had to wait until 1615 for J. B. Baumbach's printing.

The two best editions are: Historiarum Libri Decem, ed. I. Bekker, Corpus Scriptorum Historiae Byzantinae (Bonn 1843) and Historiae Demonstrationes, 2 vols., ed. E. Darko, (Budapest 1922-7). The text can also be found in J.-P. Migne, Patrologia Graeca, volume 159.

A complete English translation (by Anthony Kaldellis) of The Histories was published in two volumes in 2014 by Harvard University Press, as volumes 33 and 34 of The Dumbarton Oaks Medieval Library. Partial translations include one of Books I-III in Laonikos Chalkokondyles. A Translation and Commentary of the Demonstrations of Histories, trans. Nikolaos Nikoloudis (Athens 1996) and another of Book VIII in J. R. Melville Jones, The Siege of Constantinople: Seven Contemporary Accounts (Amsterdam 1972), pp. 42–55.