Complex sentence: He was a powerful ally of Muawiyah during the first civil war and obviously very influencial in terms of bringing Muawiyah to power.The period under Muawiya II was marked by civil wars.
Split into simpler sentences: He was a powerful ally of Muawiyah during the first civil war. And obviously he was very influencial in terms of bringing Muawiyah to power.The period under Muawiya II was marked by civil wars.