For centuries, southeastern Europe was a region of movement. This was largely – but not entirely – a consequence of its geographic location. The southeastern European peninsula links central Europe with the Near East and the southern Russian steppe. In the east, south, and west it is bounded by five seas: the Black Sea, the Sea of Marmara, the Aegean, the Ionian Sea, and the Adriatic. The straits of the Bosporus and the Dardanelles have never formed a barrier to the route between Anatolia and Europe. The coastal regions, too, were relatively accessible from the sea. And the southern Russian steppe offered open access to the Romanian lowland and, following the Danube upstream, to the Great Hungarian Low Plain, or, along the Black Sea coast, in the direction of Constantinople (Istanbul). Even the mountains (especially the Carpathians and the Balkans) were not impassable, thanks to their passes. From the age of the great migrations during the transition from antiquity to the Middle Ages down to the eve of the modern period, nomadic horseman from the southern Russian steppe lands or Asia Minor, and in their wake also settled farmers (particularly Slavs), repeatedly pushed into southeastern Europe: e.g., Huns, Avars, proto-Bulgarians, Magyars, Petchenegs, Kumans, Mongols, and Turks.

The region and its boundaries

Although the lower reaches of the Danube also functioned as a border of empires and states at various times, it was never able to present a durable barrier to migration across it. Still, ever since the onset of Christianization, a religious-cultural differentiation emerged within southeastern Europe. The Roman Church with its Latin culture prevailed north of the lower reaches of the Sava and Danube and west of the Una, a tributary of the Sava, while the region south of the Sava and Danube was shaped by the Byzantine Empire with the Eastern Church and its Greek culture, and later – during Ottoman rule – given a partial Islamic overlay. As a result, on either side of the dividing line between the two subregions we find, in transitional zones, fluctuating state, religious, cultural, and ethnic boundaries.