page_title: Expansion of Macedonia under Philip II
section_title: Greece in the early 4th century BC
hierarchical_section_title: Expansion of Macedonia under Philip II / Background / Greece in the early 4th century BC
context_page_description: Under the reign of Philip II, the kingdom of Macedonia, initially at the periphery of classical Greek affairs, came to dominate Ancient Greece in the span of just 25 years, largely thanks to the personality and policies of its king. In addition to utilising effective diplomacy and marriage alliances to achieve his political aims, Philip II was also responsible for reforming the ancient Macedonian army into an effective fighting force. The Macedonian phalanx became the hallmark of the Macedonian army during his reign and the subsequent Hellenistic period. His army and engineers also made extensive use of siege engines.
  Macedonia during the reign of Philip II was at first preoccupied by wars with marauding Illyrians and Thracians. Chief among Philip's Thracian enemies was the ruler Kersebleptes, who may have coordinated a temporary alliance with Athens. In a series of campaigns stretching from 356 to 340 BC, Philip II managed to ultimately subjugate Kersebleptes as a tributary vassal, conquering much of Thrace in the process and founding new cities there such as Philippi and Philippopolis.
context_section_description: In the aftermath of the Peloponnesian War, the militaristic city-state of Sparta had been able to impose a hegemony over the heartland of Classical Greece (the Peloponessus and mainland Greece south of Thessaly), the states of this area having been severely weakened by the war. This state of affairs was resented by many of the Greek city-states, which had traditionally been ferociously independent, and led directly to the Corinthian War of 395–387 BC. Sparta emerged from this conflict with its hegemony intact, though only as a result of Persian intervention, which led to the so-called King's Peace. The fragility of Spartan dominance had been demonstrated however, and in the next decade, the Thebans would revolt against Sparta. The Spartans were unable to successfully quell the revolt, leading to de facto Theban independence. Then, after several years of desultory conflict, the Thebans finally met the Spartans in open battle at Leuctra (371 BC), and under the leadership of Epaminondas inflicted an unprecedented defeat on the Spartan army, killing the Spartan king Cleombrotus I in the process.
  
  Following up on this victory, Epaminondas invaded Peloponnesus in 370 BC and began dismantling the basis of Spartan dominance. Spartan power rested on the forced labour of the helots of Messenia, which allowed the entire male Spartan population to dedicate themselves to warfare. This focused military training system had previously enabled Sparta to exert power out of proportion to its small population. However, after their losses at Leuctra, the Spartans were unable to resist Epaminondas's invasion, and he marched into Messenia and liberated the helots, thereby permanently crippling Sparta. The Thebans then began to extend their influence over Greece, effectively replacing the Spartan hegemony with their own. The Theban generals Pelopidas and Epaminondas campaigned all over Greece for the next 9 years to further Theban power and influence. In 362 BC, Epaminondas's fourth invasion of the Peloponnesus, which reached its climax at the Battle of Mantinea, brought almost every state in Greece into the conflict, on one side or the other. Although the Thebans and their allies were victorious at Mantinea, Epaminondas was killed, and Theban losses were heavy. Xenophon, summing up his account of Mantinea, suggests that: 
  When these things had taken place, the opposite of what all men believed would happen was brought to pass. For since well-nigh all the people of Greece had come together and formed themselves in opposing lines, there was no one who did not suppose that if a battle were fought, those who proved victorious would be the rulers and those who were defeated would be their subjects; but the deity so ordered ... that while each party claimed to be victorious, neither was found to be any better off ... but [that] there was even more confusion and disorder in Greece after the battle than before.
  — Xenophon
  The years of conflict which resulted from the Theban attempts to reorganise Greece had left much of the country war-weary and exhausted; a general peace (excluding only a recalcitrant Sparta) was therefore concluded between all the states of Greece in the aftermath of Mantinea. With the death of Epaminondas and significant loss of manpower at Mantinea, the Thebans returned to their more traditional defensive policy, and within a few years, Athens had replaced them at the pinnacle of the Greek political system, and Theban influence faded quickly in the rest of Greece. It was the Athenians, and their second League, who would be Macedon's main rivals for control of the lands of the north Aegean, and a major theme during the period was the regular state of war between Macedon and Athens.
caption: Expansion of Macedon under Philip II of Macedon