Iran is a nation in Western Asia that is also known as Persia and is officially known as the Islamic Republic of Iran. It is bounded on the west by Iraq and Turkey, on the northwest by Azerbaijan and Armenia, on the north by the Caspian Sea and Turkmenistan, on the east by Afghanistan and Pakistan, and on the south by the Gulf of Oman and the Persian Gulf. It has a total land area of 1,648,195 km2 (636,372 sq mi), making it the fourth-largest nation in Asia and the second-largest in Western Asia after Saudi Arabia. Iran has a population of 85 million people, ranking it 17th in the world. Tehran is the capital and biggest city, followed by Mashhad, Isfahan, Karaj, Shiraz, and Tabriz.
The nation is home to one of the world's oldest civilizations, dating back to the fourth millennium BC with the founding of the Elamite kingdoms. It was first unified by the Medes, an ancient Iranian people, in the seventh century BC, and reached its territorial apex in the sixth century BC, when Cyrus the Great established the Achaemenid Persian Empire, which grew to become one of history's largest empires and has been described as the world's first effective superpower. In the fourth century BC, Alexander the Great defeated the Achaemenid Empire, which was thereafter split into various Hellenistic republics. In the third century BC, an Iranian insurrection formed the Parthian Empire, which was replaced in the third century AD by the Sassanid Empire, which remained a significant international power for the following four centuries. In the seventh century AD, Arab Muslims seized the empire, resulting in the Islamization of Iran. During the Islamic Golden Age, it became a significant center of Islamic culture and scholarship, with its art, literature, philosophy, and architecture spreading across the Muslim world and beyond. Before the Seljuk Turks and Mongols invaded the area, a succession of local Iranian Muslim dynasties arose over the following two centuries. The native Safavids re-established a united Iranian state and national identity in the 15th century and converted the country to Shia Islam. Iran regained its position as a major international power under the reign of Nader Shah in the 18th century, however by the 19th century, a series of confrontations with the Russian Empire had resulted in considerable territorial losses. The Persian Constitutional Revolution occurred in the early twentieth century. Attempts to nationalize its fossil fuel supplies from Western firms ended in an Anglo-American revolution in 1953, resulting in a more authoritarian government under Mohammad Reza Pahlavi and increasing Western political dominance. In 1963, he launched a far-reaching set of changes. Following the Iranian Revolution, Ruhollah Khomeini, the country's first Supreme Leader, created the modern Islamic Republic in 1979.
Iran's government is an Islamic theocracy with features of presidential democracy, with ultimate power placed in an authoritarian "Supreme Leader," Ali Khamenei, who has held the post since Khomeini's death in 1989. The Iranian government is largely seen as authoritarian, and it has been severely chastised for substantial restrictions and violations of human rights and civil freedoms, including multiple violent suppressions of huge rallies, rigged elections, and restricted rights for women and children. It is also a focal point for Shia Islam in the Middle East, challenging the region's long-standing Arab and Sunni control. Since the Iranian Revolution, the nation has been commonly seen as Israel's and Saudi Arabia's main foe. Iran is also regarded as one of the most important participants in Middle Eastern politics, with its government directly or indirectly engaging in the bulk of recent Middle Eastern crises.
Iran is a regional and medium power with a geopolitically important position in Asia. It is a founding member of the United Nations, the European Union, the Organization of Islamic Cooperation, and the Organization of Petroleum Exporting Countries. It has abundant fossil fuel reserves, including the second-largest natural gas supply and the fourth-largest known oil reserves. The rich cultural past of the nation is represented in part through the country's 26 UNESCO World Heritage Sites. Iran, a historically multinational state, maintains a diversified country comprised of multiple ethnic, linguistic, and religious groups, the biggest of which are Persians, Azeris, Kurds, Mazandaranis, and Lurs.