Arrhidaeus (). In 357BC, he married Olympias to secure an alliance with Arybbas, the King of Epirus and the Molossians. This marriage would bear a son who would later rule as AlexanderIII (better known as Alexander the Great) and claim descent from the legendary Achilles by way of his dynastic heritage from Epirus. It is unclear whether or not the Achaemenid Persian kings influenced PhilipII's practice of polygamy, although his predecessor AmyntasIII had three sons with a possible second wife Gygaea: Archelaus, Arrhidaeus, and Menelaus. PhilipII had Archelaus put to death in 359BC, while PhilipII's other two half brothers fled to Olynthos, serving as a casus belli for the Olynthian War (349–348BC) against the Chalcidian League.

While Athens was preoccupied with the Social War (357–355 BC), PhilipII retook AmphipolisThessalian League aligned with either Phocis or Thebes. PhilipII's initial campaign against Pherae in Thessaly in 353BC at the behest of Larissa ended in two disastrous defeats by the Phocian general Onomarchus. PhilipII in turn defeated Onomarchus in 352BC at the Battle of Crocus Field, which led to PhilipII's election as leader (archon) of the Thessalian League, provided him a seat on the Amphictyonic Council, and allowed for a marriage alliance with Pherae by wedding Nicesipolis, niece of the tyrant Jason of Pherae.

Philip II had some early involvement with the Achaemenid Empire, especially by supporting satraps and mercenaries would rebelled against the central authority of the Achaemenid king. The satrap of Hellespontine Phrygia Artabazos II, who was in rebellion against Artaxerxes III, was able to take refuge as