Upon his accession to the Macedonian throne in 239 BC, Demetrios II confronted the two powerful Leagues of the Aitolians and the Achaians, who had the support of Ptolemy III of Egypt (Demetrian War). At his death ten years later, Macedonian influence in central Greece had been considerably weakened, southern Thessaly was in the hands of the Aitolians, the Dardanians threatened Macedonia from the north, and his successor was under-age.
A cousin of Demetrios, Antigonos surnamed Doson, undertook the government of the country, initially as regent, and later, in recognition of his successes, as king. Doson did in fact repulse the barbarians, restore Macedonian suzerainty in Thessaly and Macedonian influence in central Greece, and placed a large part of Karia in Asia Minor under Macedonian control.
His greatest success however consisted in obliging the Achaians to enter into an alliance with him, surrender Acrocorinth, and collaborate with him in organizing a Symmachy (alliance), in which participated the Epirotes, Phokians, Boiotians, Akarnanians, Thessalians, Achaians and Macedonians (224 BC).
In 222 BC at the battle of Sellasia, as 'hegemon' (leader) of the Symmachy, Antigonos defeated the reformist Spartan king Kleomenes III, thus securing the ascendancy of the Macedonian kingdom over southern Greece. He died in 221 BC, leaving the Macedonian throne to the seventeen-year-old Philip V, who had to confront the invasions of the Illyrians.