Back Landnahme der Slawen auf dem Balkan ALS الهجرات السلافية إلى البلقان Arabic Перасяленне славян на Балканы Byelorussian Славянско заселване на Балканите Bulgarian Doseljavanje Slavena na Balkan BS Landnahme der Slawen auf dem Balkan German Σλαβικές μεταναστεύσεις στα Βαλκάνια Greek Migraciones eslavas a los Balcanes Spanish Invasione slava della penisola balcanica Italian Colonizatio Slavica Balcaniae Latin
Early Slavs began mass migrating to Southeastern Europe between the first half of the 6th and 7th century in the Early Middle Ages. The rapid demographic spread of the Slavs was followed by a population exchange, mixing and language shift to and from Slavic.
The settlement was facilitated by the substantial decrease of the Southeastern European population during the Plague of Justinian. Another reason was the Late Antique Little Ice Age from 536 to around 660 CE and the series of wars between the Sasanian Empire and the steppe nomads against the Eastern Roman Empire. After the arrival of the Pannonian Avars in the mid-6th century, they continued to conduct incursions into Roman territory, often independently of Avar's influence. After the failed siege of Constantinople in the summer of 626, and successful revolt against the Avars, they remained in the wider Southeast Europe area after they had settled the Byzantine provinces south of the Sava and Danube rivers, from the Adriatic Sea to the Aegean and Black Sea.
Exhausted by several factors and reduced to the coastal parts of the Balkans, Byzantium was not able to wage war on two fronts and regain its lost territories, so it reconciled with the establishment of Sklavinias and created an alliance with them against the Avar and Bulgar Khaganates.