King Artaxeres I was dead and the kingdom was week. After few years Darius III became king but the empire was not too strong. The Great Alexander, prince of Greece used this time and attacked Iran with millions of soldiers. Another big reasons was that, when Greece wanted to attacked them, King Darius III went to Greece to stop them. But Alexander the Great and his soldiers, tricked Darius III and they stayed and hid at the Suez Canal  until Darius III pass them. They stayed there  for a  few days. When Darius past the canal, The Great Alexander went to Iran and destroyed everything, plus he put Takhte Jamshid(the Capital City of Iran) on fire. Some people say that Alexander didn't put Takhte Jamishd on fire on purpose, he was drunk form wine. His girl friend gave him so much wine that he could't control himself. Another reason was that some kings were not a merit and good kings and the only thing they wanted was power, they did't think about their empire and their people like king Xerxes. King Darius III  get defeated by Greece and few months later he got killed by one of his close ally. He was the last king of Hakhamaneshian Empire and Greece created a new Empire.