Even in the critical time of the Persian invasion, the Greek peoples did not act together. The experiences of political individualism were too strong to be overcome, and the rooted tradition of local autonomy successfully resisted all attempts at larger plans of unity. It is not surprising that at a time when Greek thinkers regarded the development of the city-state as the highest field for human endeavor, Greek statesmen should have seen in the expansion of their native communities only a loose federation of subject cities to be exploited financially or for the purpose of adding increased military and naval strength, and not to be subjected to any formal centralized control. As time went on the old solidarity of the Greek city-state was sapped in the fight of social classes and political parties. Not only were Athens, Sparta, and Thebes frequently at war with one another but in each one of these states there were at work factions dominated by revolutionary aims. Nothing was regarded as fixed except that the community must be self-sufficing, it mattered little in what way. It seemed as if the troubled relations of Greek political life might go on indefinitely after the Persian invasion had been repelled. No Greek statesman for a hundred and fifty years, say roughly from 500 B.C. to 350 B.C., the most brilliant period of Greek history, regarded the kingdom of Macedon as anything but a negligible quantity. Macedon itself was a land that lay on the boundaries of the Hellenic world. Its people were held to be half Hellenic and half barbarian. Even to-day scholars are not at one on the question whether the Macedonian dialect can be reckoned as properly belonging to Greek speech. But it was this alien power that ended in bringing Greece to a kind of unity, a unity based on the force of arms. The most remarkable feature of this achievement lies in the fact that it was accomplished by one man, Philip of Macedon, who began his victorious career in 359 B.C. by repressing internal disturbances at home and by dealing effectively with his warlike neighbors, the Illyrians and the Thracians. The divisions in Greece gave him the opportunity of intervention there. He posed as the friend of the oligarchic party in various Greek communities, and made it his aim to oppose by diplomacy and by war the most important center of Greek democracy, Athens. The final struggle between the free states and the Macedonian monarchy took place at the battle of Chæronea, August, 338 B.C.Philip won a decisive victory, because he had spent years in training a professional army that proved irresistible when it faced the best citizen soldiers of Athens, Thebes, and other smaller towns which, persuaded by the eloquence of Demosthenes, stood side by side in the defense of liberty. Philip survived his victory only a short time, dying in 336B.C. as the master of Greece and leaving to his son Alexander the heritage of his unique achievements.