Complex sentence: During 356 BC, Philip also conquered the town of Crenides and changed its name to Philippi: he established a powerful garrison there to control its mines, which yielded much of the gold he later used for his campaigns.
Split into simpler sentences: During 356 BC, Philip conquered the town of Crenides and changed its name to Philippi. He then established a powerful garrison there to control its mines, which yielded much of the gold he later used for his campaigns.