Complex sentence: Within six months the tiny Greek navy defeated the mighty Persian/Phoenician fleet at Salamis, and a few weeks later, the 35,000-man united Greek army, this time led by 7,000 Spartans, completely wiped out the Persians at the Battle of Plataea.
Split into simpler sentences: Within six months the tiny Greek navy defeated the mighty Persian/Phoenician fleet at the Battle of Salamis. The 35,000-man united Greek army, this time led by 7,000 Spartans, completely wiped out the Persians at the Battle of Plataea.