Complex sentence: Throughout history, political entities have expanded from basic systems of self-governance and monarchy to the complex democratic and totalitarian systems that exist today, in parallel, political systems have expanded from vaguely defined frontier-type boundaries, to the national definite boundaries existing today.
Split into simpler sentences: Throughout history, political entities have expanded from basic systems of self-governance and monarchy to the complex democratic and totalitarian systems that exist today. In parallel, political systems have expanded from vaguely defined frontier-type boundaries, to the national definite boundaries existing today.