Although the Achaean League had been fighting Macedonia for decades, Aratus sent an embassy to Antigonus III in 226 BC seeking an unexpected alliance now that the reformist king Cleomenes III of Sparta was threatening the rest of Greece in the Cleomenean War (229–222 BC). In exchange for military aid, Antigonus III demanded the return of Corinth to Macedonian control, which Aratus finally agreed to in 225 BC. Antigonus III's first move against Sparta was to capture Arcadia in the spring of 224 BC. After reforming a Hellenic league in the same vein as Philip II's League of Corinth and hiring Illyrian mercenaries for additional support, Antigonus III managed to defeat Sparta at the Battle of Sellasia in 222 BC. For the first time in Sparta's history, their city was then occupied by a foreign power, restoring Macedonia's position as the leading power in Greece. Antigonus died a year later, perhaps from tuberculosis, leaving behind a strong Hellenistic kingdom for his successor Philip V.