When Alexander lead his campaign against the Persian empire he was not only king of Macedon, but he was also the leader of the Corinthian League. However, this does not mean that the Greek Poleis were eager to join in. The campaign was indeed aimed at the archenemy of Hellas, but Alexander was also a Macedonian. Greeks and Macedonians had much in common, but Macedon had ended the power and independency of the Poleis so she was the real enemy in the eyes of many. Some groups in Athens even hoped on a Persian victory.

This is why it is not surprising that the military role of the Corinthian League in the expedition was relatively small. Only 7000 men joined the massive army of Alexander, while 50000 Greek mercenaries fought at the side of Darius. Alexander feared, and not without reason, that the remaining Greeks might attempt to revolt in the hope of restoring their independency.

To prevent this he left Antipater with an army behind in Macedon with the instructions to maintain the order in Hellas, and to reinforce the main army of Alexander if needed. Yet, the Greeks in Hellas were not the most important Greek threat to Alexander, this was Memnon, the Greek commander of the Persian forces in the Aegean. His death was a huge loss for Darius.