Greece and the Balkans 750 CE
The Balkans have been lost to Byzantine rule, and Slavs and Bulgars have settled the region.
What is happening in Greece and the Balkans in 750CE
The Balkans remained under Roman (or, as we should now call it, Byzantine) rule until the time of the emperor Heraclius (610-641). At that time, a massive invasion, led by the Avar people from central Asia but composed mostly of their Slav allies, swept down to the very walls of Constantinople itself. Like so many other invaders, they failed to capture the great city, and were defeated by Heraclius. However, the Byzantines have been unable to reimpose their authority upon most of their old Balkan territories, except near the coast. In the meantime, the earlier populations have been swamped by Slav tribes, and city life has vanished from much of the region.
In the 7th century a new people, the Bulgars, arrived from central Asia and established themselves just north of the Carpathian mountains, conquering the Slav tribes living there. They defeated a Byzantine army sent against them and were then recognized as a separate kingdom by the Byzantine emperor (681). Thereafter, the Bulgars and Byzantines have been involved in continual hostilities, with Constantinople itself sometimes being under threat.