The fall of the Roman Empire and the age of great migrations brought radical changes to the Balkan Peninsula and the Illyrian people. Barbarian tribesmen overran many rich Roman cities, destroying the existing social and economic order and leaving the great Roman aqueducts, coliseums, temples, and roads in ruins. The Illyrians gradually disappeared as a distinct people from the Balkans, replaced by the Bulgars, Serbs, Croats, and Albanians. In the late Middle Ages, new waves of invaders swept over the Albanian-populated lands. Thanks to their protective mountains, close-knit tribal society, and sheer pertinacity, however, the Albanian people developed their distinctive identity and language.

In the 4th century, barbarian tribes began to prey upon the Roman Empire, and the fortunes of the Illyrian-populated lands sagged. The Germanic Goths and Asiatic Huns were the first to arrive, invading in mid-century; the Avars attacked in A.D. 570; and the Slavic Serbs and Croats overran Illyrian-populated areas in the early 7th century. About fifty years later, the Bulgars conquered much of the Balkan Peninsula and extended their domain to the lowlands of what is now central Albania. Many Illyrians fled from coastal areas to the mountains, exchanging a sedentary peasant existence for the itinerant life of the herdsman. Other Illyrians intermarried with the conquerors and eventually assimilated. In general, the invaders destroyed or weakened Roman and Byzantine cultural centers in the lands that would become Albania.

Again during the late medieval period, invaders ravaged the Illyrian-inhabited regions of the Balkans. Norman, Venetian, and Byzantine fleets attacked by sea. Bulgar, Serb, and Byzantine forces came overland and held the region in their grip for years. Clashes between rival clans and intrusions by the Serbs produced hardship that triggered an exodus from the region southward into Greece, including Thessaly, the Peloponnese, and the Aegean Islands. The invaders assimilated much of the Illyrian population, but the Illyrians living in lands that comprise modern-day Albania and parts of Yugoslavia and Greece were never completely absorbed or even controlled.

The first historical mention of Albania and the Albanians as such appears in an account of the resistance by a Byzantine emperor, Alexius I Comnenus, to an offensive by the Vatican-backed Normans from southern Italy into the Albanian-populated lands in 1081.

The Serbs occupied parts of northern and eastern Albania toward the end of the 12th century. In 1204, after Western crusaders sacked Constantinople, Venice won nominal control over Albania and the Epirus region of northern Greece and took possession of Durrës. A prince from the overthrown Byzantine ruling family, Michael Comnenus , made alliances with Albanian chiefs and drove the Venetians from lands that now make up southern Albania and northern Greece, and in 1204 he set up an independent principality, the Despotate of Epirus, with Janina (now Ioannina in northwest Greece) as its capital. In 1272 the king of Naples, Charles I of Anjou, occupied Durrës and formed an Albanian kingdom that would last for a century. Internal power struggles further weakened the Byzantine Empire in the 14th century, enabling the Serbs' most powerful medieval ruler, Stefan Dusan, to establish a short-lived empire that included all of Albania except Durrës.

Reference

• Library of Congress Country Study of Albania