Complex sentence: Sophene was part of the kingdom of Urartu in the 8th--7th centuries BC. After unifying the region with his kingdom in the early 8th century BC, king Argishtis I of Urartu resettled many of its inhabitants to his newly built city of Erebuni.
Split into simpler sentences: Sophene was part of the kingdom of Urartu in the 8th--7th centuries BCE. After uniting the region with his kingdom in the early 8th century BCE, king Argishtis I of Urartu resettled many of its inhabitants to his newly-built city of Erebuni.