Complex sentence: The Roman victory at Sentinum started a period of integration under the Roman rulers, who established some colonies (e.g., Spoletium) and built the via Flaminia (220 BC), which became a principal vector for Roman development in Umbria.
Split into simpler sentences: The Roman victory at Sentinum started a period of integration under the Roman rulers, who established some colonies (e.g., Spoletium) and built the via Flaminia (220 BC). The via Flaminia became a principal vector for Roman development in Umbria.