The Romans were different from other major conquerors of the Balkans in that they first arrived in the west. Later attacks were launched from the southeast as well, so that by the 1st century ce the entire peninsula was under Roman control. At the height of Roman power, the Balkan peoples were the most united of any time in their history, with a common legal system, a single ultimate arbiter of political power, and absolute military security. In addition, a vibrant commerce was conducted along the Via Egnatia, a great east-west land route that led from Dyrrhachium (modern Durrës, Albania) through Macedonia to Thessalonica (modern Thessaloníki, Greece) and on to Thrace. The northwestern part of the peninsula, including Dalmatia along the Adriatic coast as well as Pannonia around the Danube and Sava rivers, became the province of Illyricum. What is now eastern Serbia was incorporated into Moesia, which reached farther eastward between the Balkan Mountains and the Danube all the way to the Black Sea. The southeastern part of the peninsula was ruled as Thrace, and the southern part was brought into Macedonia.

The Romans largely regarded the Danube River as their northern frontier, but in the 2nd and 3rd centuries their authority was extended northward into Dacia, in what is now western Romania. Dacia had been the home of a people closely related to the Thracians. The Dacians had suffered invasion by a number of peoples, including the Scythians, a mysterious people probably of Iranian origin who were absorbed into the resident population. In the 3rd century bce they managed to contain Macedonian pressure from the south, but in later years they were much less able to fend off Celtic invaders from the northwest. By the 1st century ce a substantial Dacian state extended as far west as Moravia and threatened Roman command of the Danube in the Balkans. The extension of the Dacian state and Dacian raids across the river into Moesia prompted the emperor Trajan in the first decade of the 2nd century to march into Dacia, obliterate the Dacian state and Dacian society, and establish a Roman colony that lasted until barbarian incursions forced a withdrawal back across the Danube beginning in 271.

The Orthodox east

Within the Orthodox world two monks, Cyril and Methodius, devised an alphabet that enabled their disciples to translate religious texts into Slavonic. This new alphabet enabled the establishment of a liturgical and literary language of the Balkans, but it also meant that, with Greek remaining in use in commerce and in the administration of the Byzantine Empire, the Orthodox world no longer had a common language that functioned as Latin did in the Catholic world. The lack of a universal language developed in part from a political assumption established at the very beginning of the Orthodox Christian world: that the church and the state were twin pillars of legitimate authority. Therefore, whenever a state separated from the Byzantine Empire, the impulse was for an accompanying church to be established. This association of state and church was intensified by the fear of invasion by non-Christians, a fear shared by state and church and ruler and ruled. Ruler and ruled were much less united, however, when social tensions arose—especially when, as was frequently the case, these tensions found expression in support for religious heresies. Any sign of independent thinking within the church was persecuted as a danger to temporal as well as spiritual power, and this hindered the development of those forms of intellectual exchange that later proved vital to the flowering of intellectual life in the West—Catholic Croatia-Slavonia and Dalmatia included.

The Byzantine state’s military power, like that of the Slavic kingdoms that were eventually to challenge it, rested upon landlords who held property in return for furnishing an agreed number of troops in time of war. The Byzantines developed an extensive and highly corrupt civil service, and the imperial capital’s wealth acted as a dangerous magnet, drawing ambitious Balkan leaders to it with disastrous results. There were recurrent conflicts between Constantinople and the first Bulgarian empire until the latter was crushed in the early 11th century. Although reinvigorated by its victory, the Byzantine Empire soon faced further threats. From the east came the Seljuq Turks, a Muslim people whose victory in the Battle of Manzikert in 1071 destroyed Byzantium’s security in Anatolia. Some 125 years later the threat came from Western crusaders, who in 1204 descended upon and seized the imperial capital, holding it until 1261. They also divided the empire into small fiefdoms, most of which lasted little longer than their first rulers. The Crusades had two profound effects upon the Balkans. In the first place the experience of Norman rule greatly intensified the hatred of the Eastern Orthodox against Westerners and Catholics. Second, the weakening of the empire allowed the Venetians to assume domination of seaborne trading in the eastern Mediterranean. The loss of both Anatolia and maritime supremacy deprived the empire of essential reserves of manpower, food, and wealth—losses that it could replenish only in its Balkan possessions.

In the late 12th century, attempts to levy higher taxes led the Bulgarians to revolt and establish a second empire, but this was soon enfeebled by costly wars and by the inability of the ruling Asen dynasty to control local notables. Byzantium’s life was prolonged by these inadequacies and by the inability of the Slavs to unite. In the 14th century Bulgaria was eclipsed by the rising power of Serbia, where Stefan Dušan became king in 1331. This greatest of Serbia’s medieval rulers left behind a legal code, drawn up in 1349, and a legacy of conquest that was legendary. He is also thought to have pondered the seizure of Constantinople, though by the time of his death in 1355 he had taken no positive action toward securing that goal.

The Catholic west

Political stability and unity were no more apparent among the Catholic Balkan Christians than among the Orthodox. The Croats established their own kingdom in the 10th century under Tomislav but in 1102 agreed to become part of the Hungarian monarchy. In the 14th century there was a short-lived Bosnian kingdom under the Kotromanić dynasty, but it also joined Hungary—even though Bosnia was less Catholic in its composition because many Bogomil heretics had taken refuge there.

Hungary had already established its authority as early as the 11th century in Transylvania, where it introduced both Szeklers, a Hungarian-speaking people, and German-speaking Saxons. To the east the kingdoms of Walachia and Moldavia did not emerge until the 14th century; their preoccupations were less with the Turks than with the Hungarians and the Mongols.