Philip II transformed an ineffectual and divided Macedonia into a power which dominated the Greek world. His success was based upon exploitation of Macedonia’s natural advantages and the highly professional army which he created around a core of pike-armed infantrymen, the phalanx, and his excellent cavalry. He gradually extended his empire until, after the battle of Chaeronea, it stretched from the Black Sea to the southern Peloponnese. When an assassin struck him down, he was preparing for the invasion of Persia, a project that his son Alexander III inherited.