How was Alexander able to conquer Persia?

Even with 140,000 soldiers, Darius was unable to outsmart Alexander, who perfectly executed a plan to attack Darius from the rear rather than wait to face the ruler head on at Cilicia. In addition to Alexander's cunning strategy, his use of brute force and recklessness forced Darius's men to retreat. Alexander wanted to go after and slay Darius but was called away just long enough for the defeated ruler to escape. Technically, the victory in battle meant that Alexander was now the ruler of Persia. However, Darius offered Alexander half of the kingdom as a compromise. Alexander refused, insisting that he should be the one to be known as the great king. It was ten months later before Alexander and Darius met again. This time Alexander got his way and killed Darius, effectively taking over all of Persia, Alexander's lifelong dream.