Who would invade Charlemagne's empire?

Charlemagne's empire faced invasions from several groups, notably the Vikings from the north, who raided coastal areas and river settlements, and the Magyars from the east, who conducted raids into central Europe. Additionally, the Saracens from the south posed threats to the southern territories of the empire. These invasions contributed to the fragmentation of Charlemagne's empire after his death in 814 AD.