By the conquest of the Pasargadae Fortress in 550 BC, the Achaemenid Empire was established by Cyrus II (Cyrus the Great), and after this, Iran played a very important role in the global scene. After conquering the eastern regions of Greek and the conquest of Lydia by Cyrus the Great, Persia and Greek become neighbors, and for the first time in the history, Eastern world with Persia as the leader and the West led by Greek was always in conflicts and wars.
Like Medes, the Persis inhabited the Lake Urmia and the Zagros mountain range after entering the Iranian plateau. But because of the pressures of the Medes and the Assyrian invaders they had to relocate to the south. After conquering the Pasargadae fortress, Anshan, one of the largest cities of Elamite, also conquered by the Persian Empire, Susa and Ecbatana were collapsed by Cyrus the great, eventually, Elamite civilization and Median empire were extinct. By 530 BC, Cyrus the Great had begun to expand the Achaemenid Empire, and finally, during one of these wars against massagetaes, this great king was wounded and died three days later.
After him, his son Cambyses II got the throne, he was a great king like his father and led Persian armies to conquer Egypt. Cambyses died in a tragic event, and the country was being turbulent and chaotic because his death was very suspicious. After the death of Cambyses, the throne claimants arranged rebellions and many internal conflicts occurred.
Eventually, seven Iranian commanders led by Darius the great quenched the turbulent, and in the long run, on 27th Dec. 521 BC, the last rebel was killed and Darius became king of Persia. After Cyrus the Great, Darius can be considered the most important king of the Achaemenid Empire. Darius’s effective actions are comprehended of tax cuts, judiciary reform, the foundation of regular armies, coinage, the invention of the ancient Persian language, and divide the country into 22 Satraps(provinces).
Xerxes, I was the next king of Persia. He attacked to greek and conquered Athens, burned the city, and bring the statue of the gods to Iran, these actions caused grudge and hatred of the Greeks. After the death of Xerxes, the Achaemenid Empire got weak and weaker until the permanent conflicts with Greeks and lack of internal integrity led to the collapse of the Achaemenid Empire by Alexander’s attack after the captured Persepolis.