The Second Macedonian War (200–197 BC) was fought between Macedon, led by Philip V of Macedon, and Rome, allied with Pergamon and Rhodes. The result was the defeat of Philip who was forced to abandon all his possessions in southern Greece, Thrace and Asia Minor. During their intervention, and although the Romans declared the "freedom of the Greeks" against the rule from the Macedonian kingdom, the war marked a significant stage in increasing Roman intervention in the affairs of the eastern Mediterranean which would eventually lead to their conquest of the entire region.
In 204 BC King Ptolemy IV Philopator of Egypt died, leaving the throne to his six-year-old son Ptolemy V. Philip V of Macedon and Antiochus the Great of the Seleucid Empire decided to exploit the weakness of the young king by taking Ptolemaic territory for themselves and they signed a secret pact defining spheres of interest. Philip first turned his attention to the independent Greek city states in Thrace and near the Dardanelles. His success at taking cities such as Kios worried the states of Rhodes and Pergamon who also had interests in the area.
In 201 BC, Philip launched a campaign in Asia Minor, besieging the Ptolemaic city of Samos and capturing Miletus. Again, this disconcerted Rhodes and Pergamon and Philip responded by ravaging the territory of the latter. Philip then invaded Caria but the Rhodians and Pergamenes successfully blockaded his fleet in Bargylia, forcing him to spend the winter with his army in a country which offered very few provisions.
Rome had just emerged victorious from the Second Punic War against Carthage. Up to this point Rome had taken very little interest in the affairs of the eastern Mediterranean. The First Macedonian War against Philip V had been over the issue of Illyria and was resolved by the Peace of Phoenice in 205 BC. Very little in Philip's recent actions in Thrace and Asia Minor could be said to concern the Roman Republic directly. Nevertheless, the Romans listened to the appeal from Rhodes and Pergamon and sent a party of three ambassadors to investigate matters in Greece. The ambassadors found very little enthusiasm for a war against Philip until they reached Athens. Here they met King Attalus I of Pergamon and diplomats from Rhodes. At the same time, Athens declared war on Macedon and Philip sent a force to invade Attica. The Roman ambassadors held a meeting with the Macedonian general and urged Macedon to leave the Greek cities in peace, singling out Athens, Rhodes, Pergamon, and the Aetolian League as now Roman allies and thus free from Macedonian influence and to come to an arrangement with Rhodes and Pergamon to adjudicate damages from the latest war. The Macedonian general evacuated Athenian territory and handed the Roman ultimatum to his master Philip.
Philip, who had managed to slip past the blockade and arrive back home, rejected the Roman ultimatum out of hand. He renewed his attack on Athens and began another campaign in the Dardanelles, besieging the important city of Abydus. Here, in the autumn of 200 BC, a Roman ambassador reached him with a second ultimatum, urging him not to attack any Greek state or to seize any territory belonging to Ptolemy and to go to arbitration with Rhodes and Pergamon. It was obvious that Rome was now intent on making war on Philip and at the very same time the ambassador was delivering the second ultimatum, a Roman force was disembarking in Illyria. Philip's protests that he was not in violation of any of the terms of the Peace of Phoenice he had signed with Rome were in vain.
Polybius reports that during the siege of Abydus, Philip had grown impatient and sent a message to the besieged that the walls would be stormed and that if anybody wished to commit suicide or surrender they had 3 days to do so. The citizens promptly killed all the women and children of the city, threw their valuables into the sea and fought to the last man. This story illustrates the reputation for atrocities that Philip had earned by this time during his efforts at expanding Macedonian power and influence through the conquest of other Greek cities.
Philip found himself with few active allies in Greece, but there was little enthusiasm for the Roman cause either, the Greeks remembering the frequent brutality of the legions during the First Macedonian War. Most states adopted a policy of waiting to see which way the war went. For the first two years, the Roman campaign was lacklustre. Publius Sulpicius Galba made little headway against Philip, while his successor, Publius Villius, had to deal with a mutiny among his own men. In 198 BC, Villius handed command over to Titus Quinctius Flamininus, who would prove a very different kind of general.
Flamininus was not yet thirty and was a self-proclaimed ardent Philhellene. He introduced a new Roman policy for winning the war. Up to this point, the Romans had merely ordered Philip to stop attacking the southern Greek cities ("peace in Greece"). Now Flamininus demanded that he should withdraw all his garrisons from the southern Greek cities he already held and confine himself to Macedon ("liberty for the Greeks").
Flamininus led a vigorous campaign against Philip in 198, forcing him to retreat to Thessaly. The cities of the Achaean League, traditionally favourable to Macedon, had been too busy with their war against Sparta to take any part in the Second Macedonian War so far. Roman success against Philip persuaded many of them to abandon their pro-Macedonian stance. Others, such as Argos—point of origin for the old Argead dynasty of Macedon—remained loyal to Philip.
Philip declared his willingness to make peace, but his overtures came at a critical time for Flamininus just as elections were being held in Rome. Flamininus was eager to take the credit for ending the war but he did not yet know whether his command would be prolonged. He decided to negotiate with Philip while he awaited the outcome of the elections. If they meant he was to be recalled to Rome, then he would make a quick peace deal with the Macedonian. If, on the other hand, his command was extended, then he intended to break off the negotiations and declare war on Philip again. Flamininus and Philip met at Nicaea in Locris in November 198. To prolong the proceedings, Flamininus insisted that all his allies should be present at the negotiations. Flamininus reiterated his demands that Philip should withdraw from the whole of Greece. Philip, who was prepared to give up all his recent conquests in Thrace and Asia Minor, could not go this far. Flamininus persuaded him that the problem was the Greek states who were insisting on this point and suggested he should send an embassy to the Roman Senate. Philip followed his advice but at this moment Flamininus learned that his command had been extended and his friends in Rome successfully interfered with the Macedonian negotiations in Rome so the war could continue.
Seeing things were going Rome's way, Philip's few remaining allies abandoned him (with the exception of Acarnania) and he was forced to raise an army of 25,000 mercenaries. The legions of Titus confronted and defeated Philip at the Aous, However the decisive encounter came at Cynoscephalae in Thessaly in June 197 BC, when the legions of Flamininus defeated Philip's Macedonian phalanx. Philip was forced to sue for peace on Roman terms.
An armistice was declared and peace negotiations were held in the Vale of Tempe. Philip agreed to evacuate the whole of Greece and relinquish his conquests in Thrace and Asia Minor. Flamininus' allies in the Aetolian League also made further territorial claims of their own against Philip but Flamininus refused to back them. The treaty was sent to Rome for ratification. The Senate added terms of its own: Philip must pay a war indemnity and surrender his navy (although his army was untouched). In 196, peace was finally agreed and at the Isthmian Games that year Flamininus proclaimed the liberty of the Greeks to general rejoicing of those who were attending the Games. Nevertheless, the Romans kept garrisons in key strategic cities which had belonged to Macedon – Corinth, Chalcis and Demetrias – and the legions were not completely evacuated until 194.