Alexander and The Seleucids
Alexander conquered the Achaemenian Empire systematically. He moved from Asia Minor to Syria, Palestine and Egypt, to Mesopotamia, to Iran proper, on to Afghanistan, Transoxiana and finally to Achaemenian India, investing one satrapy after the other, against continuous resistance, to leave no remnant that could reconstitute Achaemenian power. It must be realized that in conquering the “world” he never went beyond the reaches of Achaemenian Persia. When he tried to do so in India, his troops refused to go no. They had done what they set out to do, to conquer Persia. What more did he want? How much longer should they be away from home?
Alexander had no time to consolidate his power administratively, although he tried to go one step further than the Persians by advocating integration and racial mixing by mass intermarriage. The empire of Alexander after his death in Babylon was divided amongst his successor generals into several parts, of which central Iran under his infant son by his Persian wife was one.