Complex sentence: Then he began acting as an independent ruler and eventually succeeded in gaining control of much of what is the area of present Iran as well as portions of Afghanistan and Pakistan and became the sovereign monarch of the first Iranian dynasty in post-Islam era.
Split into simpler sentences: Then he began acting as an independent ruler and eventually succeeded in gaining control of much of what is the area of present Iran as well as Afghanistan and Pakistan. He became the sovereign monarch of the first Iranian dynasty in post-Islam era.