Complex sentence: At the time of the Magyar invasion, the Carpathian Basin was divided among several powers, because following the collapse of the Avar Empire around 800, the neighboring powers had occupied only parts of its territory.
Split into simpler sentences: At the time of the Magyar invasion, the Carpathian Basin was divided among several powers. Following the collapse of the Avar Empire around 800, the neighboring powers had occupied only parts of its territory.