Expansion of Macedonia under Philip II
The Third Sacred War (often just called 'the' Sacred War) broke out in 356 BC, and would present Philip with his first real opportunity to expand his influence into the affairs of central and southern Greece. The war was ostensibly caused by the refusal of the Phocian Confederation to pay a fine imposed on them in 357 BC by the Amphictyonic League, a pan-Greek religious organisation which governed the most sacred site in Ancient Greece, the Temple of Apollo at Delphi. Behind the religious element, there probably lay a display of "realpolitik" in bringing charges against the Phocians, instigated by the Thebans. At this time, Thebes controlled a majority of the votes in the council, and at the autumn meeting in 357 BC, the Thebans were able to have both the Phocians (for the cultivation of the sacred land) and the Spartans (for occupying Thebes some 25 years previously) denounced and fined. Since the fines for both parties were "unjustifiably harsh", the Thebans probably expected neither party to pay, and thus to be able to declare a "sacred war" on either.
Third Sacred War
Athens and Macedon had been at war since 356 BC, after Philip's capture of the Athenian colonies of Pydna and Potidea. Philip had then been drawn into the Sacred War, on behalf of the Thessalians, as described above. Since Athens was also a combatant in the Sacred War, the war between Athens and Macedon was inextricably linked with the progress of the Sacred War. In 352 BC, Philip's erstwhile ally, the Chalkidian League (led by Olynthos), alarmed by Philip's growing power, sought to ally themselves with Athens, in clear breach of their alliance with Philip. In response, Philip attacked Chalkidiki in 349 BC, and by 348 BC, had completely destroyed the Chalkidian League, razing Olynthos in the process. The prominent Athenian politician Philocrates had suggested offering Philip peace in 348 BC, during the Olynthian war. The war between Athens and Philip thus continued through 347 BC, as did the Sacred War.