and its large reserves of fossil fuels - including the world's largest natural gas supply and the fourth largest proven oil reserves - exert considerable influence in international energy security and the world economy.
The term Iran derives directly from Middle Persian Ērān, first attested in a third-century inscription at Rustam Relief, with the accompanying Parthian inscription using the term Aryān, in reference to the Iranians.
An Iranian rebellion established the Parthian Empire in the third century BCE, which was succeeded in the third century CE by the Sasanian Empire, a leading world power for the next four centuries.
Arab Muslims conquered the empire in the seventh century CE, and the subsequent Islamization of Iran led to the decline of the once dominant Zoroastrian religion.
Tehran is the political and economic center of Iran, and the largest and most populous city in Western Asia with more than 8.8 million residents in the city and 15 million in the larger metropolitan area.
In 550 BC, Cyrus the Great, the son of Mandane and Cambyses I, took over the Median Empire, and founded the Achaemenid Empire by unifying other city-states.
to the north by the Caspian Sea, to the northeast by Turkmenistan, to the east by Afghanistan and Pakistan, to the south by the Persian Gulf and the Gulf of Oman, and to the west by Turkey and Iraq.
Its central location in Eurasia and Western Asia, and its proximity to the Strait of Hormuz, give it geostrategic importance.
In 334 BC, Alexander the Great invaded the Achaemenid Empire, defeating the last Achaemenid emperor, Darius III, at the Battle of Issus.
Following the premature death of Alexander, Iran came under the control of the Hellenistic Seleucid Empire.
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As the Iranians dispersed into the wider area of Greater Iran and beyond, the boundaries of modern-day Iran were dominated by Median, Persian, and Parthian tribes.