Philip's military skills and expansionist vision of Macedonian greatness brought him early success. He first had to re-establish a situation which had been greatly worsened by the defeat against the Illyrians in which King Perdiccas himself had died.
The Paionians and the Thracians had sacked and invaded the eastern regions of the country, while the Athenians had landed, at Methoni on the coast, a contingent under a Macedonian pretender called Argeus. Using diplomacy, Philip pushed back Paionians and Thracians promising tributes, and crushed the 3,000 Athenian hoplites (359).
Momentarily free from his opponents, he concentrated on strengthening his internal position and, above all, his army. His most important innovation was doubtless the introduction of the phalanx infantry corps, armed with the famous sarissa, an exceedingly long spear, at the time the most important army corps in Macedonia.