After Alexander's defeat, the Macedonian forces, now led by a junta of the late king's top generals, retreat to Macedon with the Persian army in hot pursuit. The situation appears hopeless, but Darius's arrogance and assurance of victory leads him to lead the Persians straight into a trap set by the desperate Macedonian command. In the rugged terrain of Asia Minor the superior Persian soldiers suffer a crushing loss, and Darius himself dies on the battlefield. After such an unexpected battle the two sides make peace and history is left to unfold in a very different way.
Though the Persians manage to regain all of the territory they lost to Alexander, the war with Macedon has planted the seeds for their empire's destruction. Darius's successors will attempt to rule a Persia more unstable than ever, with disloyal satraps waiting for a chance to rebel and a gradually eroding central authority. After several generations of stagnation, the Persian Empire implodes around 200 BC, and several subject nations take the chance to break away.
In Greece the power vacuum created by defeat at Gaugamela gives the old city-states new impetus to rebel. After several anarchic civil wars, the countries of Greece, exhausted and surrounded by enemies, reconstitute themselves as a new Hellenic League.
Further to the West Alexander's loss also brings changes. With the Pyrrhic Wars butterflied away, Roman expansion and rise is considerably slower. By the time the Romans secure Italy, Carthage has grown too powerful to destroy. The two increasingly bitter rivals nevertheless fight several bloody and inconclusive wars as both expand into barbarian lands.
By 100 AD the world looks set to change. Persia has risen from the ashes, and reabsorbed several former defectors, pushing back into the Fertile Crescent and India. Rome, which has remained a republic, has, by virtue of new territories in Gaul and Britain, began to outpace the Carthaginians, who along with the Greeks grow increasingly wary. Whether in the Hellenized West or in the East, a mighty shift in the status quo is on the cusp of unfolding.