The league was the first Greek ally of the Roman Republic, siding with the Romans during the First Macedonian War (215-205 BC), and helping to defeat Philip V of Macedon at the Battle of Cynoscephalae in 197 BC, during the Second Macedonian War. However, it grew increasingly hostile to Roman involvement in Greek affairs and only a few years later sided with Antiochus III, the anti-Roman king of the Seleucid Empire, during the Roman-Syrian War. The defeat of Antiochus in 189 BC robbed the league of its principal foreign ally and made it impossible to stand alone in continued opposition to Rome. The league was forced to sign a peace treaty with Rome that made it a subject ally of the republic. Although it continued to exist in name, the power of the league was broken by the treaty and it never again constituted a significant political or military force.