The reign of Vladislav’s son and successor, Stephen Uroš I (1242-76), was characterized by economic development and the strengthening of the internal administration. In external affairs he made no conquests, but defeated a combination of the Bulgarians with Ragusa against him, and after the war the Bulgarian ruler married his daughter. In his wars against Hungary he was unsuccessful, and the Magyars remained in possession of a large part of northern Serbia. In 1276 he was deposed by his son, Stephen Dragutin, who in his turn, after an unsuccessful war against the Greeks, again masters of Constantinople since 1261, was deposed and succeeded by his brother, Stephen Uroš II, named Milutin, in 1282. This king ruled from 1282 till 1321, and during his reign the country made very great material progress; its mineral wealth especially, which included gold and silver mines, began to be exploited. He extended the boundaries of his kingdom in the north, making the Danube and the Save the frontier. The usual revolt against paternal authority was made by his son Stephen, but was unsuccessful, and the rebel was banished to Constantinople.

It was the custom of the Serbian kings to give appanages to their sons, and the inevitable consequence of this system was the series of provincial rebellions which occurred in almost every reign. When the revolt succeeded, the father (or brother) was granted in his turn a small appanage. In this case it was the son who was exiled, but he was recalled in 1319 and a reconciliation took place. Milutin died in 1321 and was succeeded by his son, Stephen Uroš III, who reigned till 1331. He is known as Stephen Dečanski, after the memorial church which he built at Dečani in western Serbia. His reign was signalized by a great defeat of the combined Bulgarians and Greeks at Kustendil in Macedonia in 1330. The following year his son, Stephen Dušan, rebelled against him and deposed him. Stephen Dušan, who reigned from 1331 till 1355, was Serbia’s greatest ruler, and under him the country reached its utmost limits. Provincial and family revolts and petty local disputes with such places as Ragusa became a thing of the past, and he undertook conquest on a grand scale. Between 1331 and 1344 he subjected all Macedonia, Albania, Thessaly, and Epirus. He was careful to keep on good terms with Ragusa and with Hungary, then under Charles Robert. He married the sister of the Bulgarian ruler, and during his reign Bulgaria was completely under Serbian supremacy. The anarchy and civil war which had become perennial at Constantinople, and the weakening of the Greek Empire in face of the growing power of the Turks, no doubt to some extent explain the facility and rapidity of his conquests; nevertheless his power was very formidable, and his success inspired considerable alarm in western Europe. This was increased when, in 1345, he proclaimed his country an empire. He first called together a special Church council, at which the Serbian Church, an archbishopric, whose centre was then at Peć (in Montenegro, Ipek in Turkish), was proclaimed a Patriarchate, with Archbishop Joannice as Patriarch; then this prelate, together with the Bulgarian Patriarch, Simeon, and Nicholas, Archbishop of Okhrida, crowned Stephen Tsar of the Serbs, Bulgars, and Greeks. Upon this the Patriarch of Constantinople gave himself the vain satisfaction of anathematizing the whole of Serbia, as a punishment for this insubordination.

In 1353 the Pope, Innocent VI, persuaded King Louis of Hungary to undertake a crusade against Serbia in the name of Catholicism, but Stephen defeated him and re-established his frontier along the Save and Danube. Later he conquered the southern half of Dalmatia, and extended his empire as far north as the river Cetina. In 1354 Stephen Dušan himself approached the Pope, offering to acknowledge his spiritual supremacy, if he would support him against the Hungarians and the Turks. The Pope sent him an embassy, but eventually Stephen could not agree to the papal conditions, and concluded an alliance, of greater practical utility, with the Venetians. In 1355, however, he suddenly died, at the age of forty-six, and thus the further development and aggrandisement of his country was prematurely arrested.

Stephen Dušan made a great impression on his contemporaries, both by his imposing personal appearance and by his undoubted wisdom and ability. He was especially a great legislator, and his remarkable code of laws, compiled in 1349 and enlarged in 1354, is, outside his own country, his greatest title to fame. During Stephen Dušan’s reign the political centre of Serbia, which had for many years gradually tended to shift southwards towards Macedonia, was at Skoplje (Üsküb in Turkish), which he made his capital. Stephen Dušan’s empire extended from the Adriatic in the west to the river Maritsa in the east, from the Save and Danube in the north to the Aegean; it included all the modern kingdoms of Serbia, Montenegro, Albania, and most of Greece, Dalmatia as far north as the river Cetina, as well as the fertile Morava valley, with Nish and Belgrade—the whole eastern part of Serbia, which had for long been under either Bulgar or Magyar control. It did not include the cities of Salonika or Ragusa, nor any considerable part of the modern kingdom of Bulgaria, nor Bosnia, Croatia, North Dalmatia, nor Slavonia (between the Save and Drave), ethnologically all purely Serb lands. From the point of view of nationality, therefore, its boundaries were far from ideal.

Stephen Dušan was succeeded by his son, known as Tsar Uroš, but he was as weak as his father had been strong. Almost as soon as he succeeded to the throne, disorders, rebellions, and dissensions broke out and the empire rapidly fell to pieces. With Serbia, as with Bulgaria, the empire entirely hinged on the personality of one man, and when he was gone chaos returned. Such an event for Serbia at this juncture was fatal, as a far more formidable foe than the ruler’s rebellious relations was advancing against it. The Turkish conquests were proceeding apace; they had taken Gallipoli in 1354 and Demotika and Adrianople in 1361. The Serbs, who had already had an unsuccessful brush with the advance guard of the new invaders near Demotika in 1351, met them again on the Maritsa river in 1371, and were completely defeated. Several of the upstart princes who had been pulling Stephen Dušan’s empire to pieces perished, and Tsar Uroš only survived the battle of the Maritsa two months; he was unmarried, and with him died the Nemanja dynasty and the Serbian Empire.

After this disaster the unity of the Serbian state was completely destroyed, and it has never since been restored in the same measure.

That part of the country to the south of Skoplje fell completely under Turkish control; it was here that the famous national hero, Marko Kraljević (or King’s son), renowned for his prowess, ruled as a vassal prince and mercenary soldier of the Turks; his father was one of the rebel princes who fell at the battle of the river Maritsa in 1371. North of Skoplje, Serbia, with Kruševac as a new political centre, continued to lead an independent but precarious existence, much reduced in size and glory, under a native ruler, Prince Lazar; all the conquests of Stephen Dušan were lost, and the important coastal province of Zeta, which later developed into Montenegro, had broken away and proclaimed its autonomy directly after the death of Tsar Uroš.

In 1375 a formal reconciliation was effected with the Patriarch of Constantinople; the ban placed on the Serbian Church in 1352 was removed and the independence of the Serbian Patriarchate of Peć (Ipek) recognised. Meanwhile neither Greeks, Bulgars, nor Serbs were allowed any peace by the Turks.

In 1389 was fought the great battle of Kosovo Polje, or the Field of Blackbirds, a large plain in Old Serbia, at the southern end of which is Skoplje. At this battle Serbian armies from all the Serb lands, including Bosnia, joined together in defence of their country for the last time. The issue of the battle was for some time in doubt, but was decided by the treachery and flight at the critical moment of one of the Serb leaders, Vuk Branković, son-in-law of Prince Lazar, with a large number of troops. Another dramatic incident was the murder of Sultan Murad in his tent by another Serbian leader, Miloš Obilić, who, accused of treachery by his own countrymen, vowed he would prove his good faith, went over to the Turks and, pretending to be a traitor, gained admission to the Sultan’s presence and proved his patriotism by killing him. The momentary dismay was put an end to by the energetic conduct of Bayezid, son of Murad, who rallied the Turkish troops and ultimately inflicted total defeat on the Serbians. From the effects of this battle Serbia never recovered; Prince Lazar was captured and executed; his wife, Princess Milica, had to give her daughter to Bayezid in marriage, whose son thus ultimately claimed possession of Serbia by right of inheritance. Princess Milica and her son Stephen continued to live at Kruševac, but Serbia was already a tributary of Turkey. In the north, Hungary profited by the course of events and occupied Belgrade and all northern Serbia, but in 1396 the Turks defeated the Magyars severely at the battle of Nikopolis, on the Danube, making the Serbs under Stephen fight on the Turkish side. Stephen also had to help Sultan Bajazet against the Tartars, and fought at the battle of Angora, in 1402, when Tamerlane captured Bayezid.

After Stephen returned to Serbia he made an alliance with Hungary, which gave him back Belgrade and northern Serbia; it was at this time (1403) that Belgrade first became the capital, the political centre having in the course of fifty years moved from the Vardar to the Danube. The disorders which followed the defeat of Bayezid gave some respite to the Serbs, but Sultan Murad II (1421-51) again took up arms against him, and invaded Serbia as far as Kruševac.