The great raid mounted by the Mongols in 1240-1241 had brought substantial devastation and political and economic disruption to the northern Balkan region. Bulgaria collapsed into civil war and factionalism and was only reunited in the later 1320s when the Byzantine empire, itself rent by civil war, ceded substantial territory to the Bulgar Tsar Mihail Sisman, who had been elected by the boyars (nobles) as the best candidate to lead them. A disastrous alliance with Byzantium against the Serbs ended in defeat and the death of Sisman in 1330. Thereafter, Bulgaria was a subordinate in the Balkan scheme of things to its increasingly powerful Serb neighbour, and a victim of factional rivalries and strife. By the 1340s the Dobrudja had broken away under an independent boyar, Balik, whose successor, Dobrotitsa gave his name to the region, and the region around Vidin had also broken away. This situation had made the Serbian expansion under Stefan Dusan straightforward, but when Dusan died in 1355 his state broke up. His son and successor (Stefan Uros V [1355-1371]) was unable to maintain his authority, and instead of the powerful empire which he inherited at his accession there soon appeared a whole group of petty principalities which competed with one another for local pre-eminence. While the central Serbian regions remained under the Tsar’s rule, the most recently acquired Greek regions in Epiros and Thessaly split away, as did the Albanian districts. Venetian control of much of the coast served to foment further discontent and rivalry among the local lords. Autonomous Serb rulers established their own principalities in the south, in Macedonia and adjacent regions, where some seven separate statelets were established. And as all this occurred, the Hungarians again pushed into the northwestern parts of Serbian-held territory, taking Belgrade and the surrounding districts.
As we have already seen, the northern trans-Danubian territories of the Bulgarian state had become independent by the 1340s in the context of both a weak and divided Bulgaria and the Hungarian succession struggle. The overall picture which thus emerges in the Balkans is one of extreme fragmentation. No major powerful state survived into the late fourteenth century, with the exception, possibly, of Hungary, which geographically does not really count as a ‘Balkan state’. The Byzantine empire, wrecked by civil wars and reduced territorially to a few Aegean isles, the southern Peloponnese and Constantinople with Thrace, was no longer a force to be reckoned with, and the arrival of the Turks on a permanent basis from 1354 introduced a further complication into this situation.
In the course of his wars with John V Palaiologos, the Emperor John VI Kantakouzenos employed both western and eastern mercenary troops. In 1345 he requested, and received, military aid from his ally, the Ottoman Sultan Orhan I (13241360), and again in 1349, to combat the threat from Serbia, he received further aid. Again in 1354 he requested help, but this time the Ottoman troops entrenched themselves on the Gallipoli peninsula, which became a permanent base. The fragmented political situation in the Balkans after Dusan’s death and the lack of any serious opposition meant that the Ottoman troops now had a free hand to raid wherever they wished; it also meant the beginnings of a permanent Ottoman presence in Europe.
The Ottoman Sultanate is named after its eponymous founder, Osman (1284-1324), a Seljuk warlord in northwestern Asia Minor who prosecuted the war against Byzantium with great zeal, attracting in consequence a reputation as a ghazi, a fighter for the faith, along with large numbers of independent warriors, who wished to join him as much for the booty as for their religion. Early in the reign of his son, Orhan, the Ottomans took Bursa, the last Byzantine fortress in Asia Minor. Ottoman military organisation was effective, and under Orhan’s successor Murad I a new phase of expansion, directed from the newly-established European bridgehead at the Serbs, Byzantines and Bulgars, was set in train. Adrianople (Edirne) was taken in 1365 and became the new Ottoman capital; new heavy infantry units, referred to as janissaries (Turk. yeni ceri, ‘new guard’) recruited from captives, bolstered the existing light cavalry of the Ottoman forces, and by the early 1370s most of Bulgaria south of the Balkan mountains had been conquered, local Serbian forces had been crushed and Macedonia incorporated, and by 1386 Ottoman troops had taken Nis and were poised to enter the heartlands of Serbia. The Serbian ruler Lazar was reduced to vassal status and, alongside many other defeated nobles and petty lords, served in the ranks of Ottoman allies in the campaigns that followed. When Lazar organised an alliance to cast off Ottoman rule both Murad and Lazar fought in their respective armies at the battle of Kosovo Polje in 1389, and both died. Serbia fell into further anarchy as a result, and by 1393 Bulgaria had been incorporated entirely into the Ottoman dominion. The unsuccessful ‘crusade’ led by Sigismund of Hungary, aimed at throwing back the Ottoman advance, ended in a crushing defeat at Nikopolis in 1396. The result of the Mongol (Timurid) invasion of Asia Minor and the Ottoman defeat at the battle of Ankara in 1402 was internal strife in the Ottoman court and a temporary halt to their advance in the Balkans. Serbia was able to restore some order and re-assert its territorial claims on the territories recently lost. But under Mehmet I (1413-1421) the Ottomans were able to restore the situation to their advantage, and in the reign of Murad II (1421-1451) began once more to move forward. Thessalonica and much of the Aegean were taken in the 1430s; Hungary was raided, and the last crusade, led by the Hungarian general Janos Hunyadi, was defeated near Varna in 1444. Of the Byzantine empire only Constantinople and the isles of Lemnos and Thasos remained, apart from the Peloponnese. Constantinople finally fell in 1453, and shortly afterwards the Peloponnese was also incorporated into the Ottoman lands. The final reduction of Serbia had taken place by 1458, the defeat and occupation of Bosnia was completed by 1461 (the same year in which Trebizond finally surrendered), and by 1463 Albanian resistance had been crushed. The Byzantine empire had been replaced by the Ottoman.