Battle of Crocus Field
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 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.
Macedonia (ancient kingdom)
Philip II then involved Macedonia in the Third Sacred War (356–346BC). It began when Phocis captured and plundered the temple of Apollo at Delphi instead of submitting unpaid fines, causing the Amphictyonic League to declare war on Phocis and a civil war among the members of the Thessalian 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.