Complex sentence: The Akkadian Empire--which in 2300 BC was the second civilization to subsume independent societies into a single state (the first being ancient Egypt at around 3100 BC)--was brought low by a wide-ranging, centuries-long drought.
Split into simpler sentences: The Akkadian Empire in 2300 BC was the second civilization to subsume independent societies into a single state (the first being ancient Egypt at around 3100 BC). It has been claimed that the collapse of the state was influenced by a wide-ranging, centuries-long drought.