A Short History of the World by H.G. Wells

From 431 to 404 B.C. the Peloponnesian War wasted Greece. Meanwhile to the north of Greece, the kindred country of Macedonia was rising slowly to power and civilization. The Macedonians spoke a language closely akin to Greek, and on several occasions Macedonian competitors had taken part in the Olympic games. In 359 B.C. a man of very great abilities and ambition became king of this little country--Philip. Philip had previously been a hostage in Greece; he had had a thoroughly Greek education and he was probably aware of the ideas of Herodotus--which had also been developed by the philosopher Isocrates--of a possible conquest of Asia by a consolidated Greece.

He set himself first to extend and organize his own realm and to remodel his army. For a thousand years now the charging horse-chariot had been the decisive factor in battles, that and the close-fighting infantry. Mounted horsemen had also fought, but as a cloud of skirmishers, individually and without discipline. Philip made his infantry fight in a closely packed mass, the Macedonian phalanx, and he trained his mounted gentlemen, the knights or companions, to fight in formation and so invented cavalry. The master move in most of his battles and in the battles of his son Alexander was a cavalry charge. The phalanx _held_ the enemy infantry in front while the cavalry swept away the enemy horse on his wings and poured in on the flank and rear of his infantry. Chariots were disabled by bowmen, who shot the horses.