Complex sentence: Flavius Phocas Augustus, ("Phokas"; reigned 602--610), usurped the Byzantine throne from the Emperor Maurice, and was himself overthrown by Heraclius after losing a civil war.
Split into simpler sentences: Flavius Phocas Augustus, ("Phokas") was Byzantine Emperor from 602 to 610. He usurped the throne from the Emperor Maurice, and was himself overthrown by Heraclius after losing a civil war.