Complex sentence: When the Romans destroyed the Antigonid dynasty of Macedon in 168 BC and divided it into four separate states ("merides"), it was Amphipolis and not Philippi that became the capital of the eastern Macedonian state.
Split into simpler sentences: When the Romans destroyed the Antigonid dynasty of Macedon in 168 BC, they divided the city-state into four separate states ("merides"). It was Amphipolis and not Philippi that became the capital of the eastern Macedonian state.