Complex sentence: This was fully and permanently realized in 338 when Philip II of Macedon defeated the Thebans at the Battle of Chaeronea and his son, Alexander the Great altogether destroyed Thebes-enabling the exiled Plateans to return and rebuild their city with no apprehension of further exile.
Split into simpler sentences: This was fully and permanently realized after Philip II of Macedon defeated the Thebans at the Battle of Chaeronea and his son, Alexander the Great altogether destroyed Thebes. This enabled the exiled Plateans to return and rebuild their city in 338 BC, with no apprehension of a further exile.