Complex sentence: In 146 B.C. Sellasia became part of the Roman Empire and when the empire divided into east and west, it became part of theEastern Roman Empire now referred to as the Byzantine Empire.
Split into simpler sentences: In 146 B.C. Sellasia became part of the Roman Empire. When the empire divided into east and west, it became part of theEastern Roman Empire now referred to as the Byzantine Empire.