Iran, also called Persia and officially known as the Islamic Republic of Iran , is a country in Western Asia. With over 81 million inhabitants, Iran is the world's 18th most populous country. Comprising a land area of 1648195 km2, it is the second largest country in the Middle East and the 17th largest in the world. Iran is bordered to the northwest by Armenia and the Republic of Azerbaijan, 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. The country's central location in Eurasia and Western Asia, and its proximity to the Strait of Hormuz, give it geostrategic importance. Tehran is the country's capital and largest city, as well as its leading economic and cultural center.
Iran is home to one of the world's oldest civilizations, beginning with the formation of the Elamite kingdoms in the fourth millennium BCE. It was first unified by the Iranian Medes in the seventh century BCE, reaching its greatest territorial size in the sixth century BCE, when Cyrus the Great founded the Achaemenid Empire, which stretched from Eastern Europe to the Indus Valley, becoming one of the largest empires in history. The Iranian realm fell to Alexander the Great in the fourth century BCE and was divided into several Hellenistic states. An Iranian rebellion culminated in the establishment of the Parthian Empire, 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. The Islamization of Iran led to the decline of Zoroastrianism, which was by then the country's dominant religion, and Iran's major contributions to art and science spread within the Muslim rule during the Islamic Golden Age. After two centuries, a period of various native Muslim dynasties began, which were later conquered by the Seljuq Turks and the Ilkhanate Mongols. The rise of the Safavids in the 15th century led to the reestablishment of a unified Iranian state and national identity, with the country's conversion to Shia Islam marking a turning point in Iranian and Muslim history. Under Nader Shah, Iran was one of the most powerful states in the 18th century, though by the 19th century, a series of conflicts with the Russian Empire led to significant territorial losses. The Iranian Constitutional Revolution in the early 20th century led to the establishment of a constitutional monarchy and the country's first legislature. A 1953 coup instigated by the United Kingdom and the United States resulted in greater autocracy and growing Western political influence. Subsequent widespread dissatisfaction and unrest against the monarchy led to the 1979 Revolution and the establishment of an Islamic republic, a political system that includes elements of a parliamentary democracy vetted and supervised by a theocracy governed by an autocratic "Supreme Leader". During the 1980s, the country was engaged in a war with Iraq, which lasted for almost eight years and resulted in a high number of casualties and economic losses for both sides.
The sovereign state of Iran is a founding member of the UN, ECO, NAM, OIC, and OPEC. It is a major regional and middle power, and its large reserves of fossil fuels – which include 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 country's rich cultural legacy is reflected in part by its 22 UNESCO World Heritage sites, the third largest number in Asia and 11th largest in the world. Iran is a multicultural country comprising numerous ethnic and linguistic groups, the largest being Persians (61%), Azeris (16%), Kurds (10%), and Lurs (6%). Organizations including Amnesty International and Human Rights Watch have strongly criticized Iran's women's rights record.
The term Iran derives directly from Middle Persian, first attested in a third-century inscription at Rustam Relief, with the accompanying Parthian inscription using the term , in reference to the Iranians. The Middle Iranian ērān and aryān are oblique plural forms of gentilic nouns ēr- (Middle Persian) and ary- (Parthian), both deriving from Proto-Iranian *arya- (meaning "Aryan", i.e. "of the Iranians"), recognized as a derivative of Proto-Indo-European , meaning "one who assembles (skilfully)". In the Iranian languages, the gentilic is attested as a self-identifier, included in ancient inscriptions and the literature of the Avesta, and remains also in other Iranian ethnic names Alan (Ир ) and Iron (Ирон).
Historically, Iran has been referred to as Persia by the West, due mainly to the writings of Greek historians who referred to all of Iran as (from Old Persian 𐎱𐎠𐎼𐎿 ), meaning "land of the Persians", while Persis itself was one of the provinces of ancient Iran that is today defined as Fars. As the most extensive interaction the Ancient Greeks had with any outsider was with the Persians, the term persisted, even long after the Greco-Persian Wars (499–449 BC).
In 1935, Reza Shah requested the international community to refer to the country by its native name, Iran, effective March 22 that year. As The New York Times explained at the time, "At the suggestion of the Persian Legation in Berlin, the Tehran government, on the Persian New Year, Nowruz, March 21, 1935, substituted Iran for Persia as the official name of the country." Opposition to the name change led to the reversal of the decision, and Professor Ehsan Yarshater, editor of Encyclopædia Iranica, propagated a move to use Persia and Iran interchangeably. Today, both Iran and Persia are used in cultural contexts, while Iran remains irreplaceable in official state contexts.
Historical and cultural usage of the word Iran is not restricted to the modern state proper. "Greater Iran" (Irānzamīn or Irān e Bozorg) refers to territories of the Iranian cultural and linguistic zones. In addition to modern Iran, it includes portions of the Caucasus, Anatolia, Mesopotamia, Afghanistan, and Central Asia.