Complex sentence: In 29 BC, Octavian returned to Rome as the unchallenged master of the state, were he eventually enacted a series of constitutional reforms, the most important of which occured in 27 BC, which overthrew the old republic.
Split into simpler sentences: In 29 BC, Octavian returned to Rome as the unchallenged master of the state. He eventually enacted a series of constitutional reforms, the most important of which occured in 27 BC, which overthrew the old republic.