Alexander marches east, hoping for a confrontation with Darius's forces. If Darius were to adopt a "retreat & burn" strategy, Alexander would soon be in trouble logistically. Alexander gets his wish. There is a major battle at Gaugamela. Although outnumbered by about 6 to 1, Alexander's cavalry appears to make the difference, and soon Darius is fleeing for his life. Alexander gives chase, but fails to overtake him.

Alexander then marches on to Babylon where he is received, without a fight, as the new leader. A similar reception awaits him at Susa, and at Peresepolis. The ratio of battles to surrender is low. This is also part of the explanation for his success. On the other hand, surrender makes sense for the cities, since otherwise they will be destroyed. There is not a strong sense of national identity - rather each city is in large part on its own.

Darius is murdered by his own troops and Alexander may now claim to be king of the region. He then begins to continue further east into Persia.