Complex sentence: After the collapse of the Roman empire, Ostrogoths and Byzantines struggled for the supremacy in the region; the Lombards founded the duchy of Spoleto, covering much of today's Umbria.
Split into simpler sentences: After the collapse of the Roman empire, Ostrogoths and Byzantines struggled for the supremacy in the region. The Lombards founded the duchy of Spoleto, covering much of today's Umbria.