Iran, officially the Islamic Republic of Iran, formerly known internationally as Persia until 1935, is a country in Central Eurasia, located on the northeastern shore of the Persian Gulf. The name Iran is a cognate of Aryan, and means "Land of the Aryans".
The 18th largest country in the world in terms of area at 1,648,195 km², Iran has a population of over seventy million. It is a country of special geostrategic significance due to its central location in Eurasia. Iran is bordered on the north by Armenia, Azerbaijan and Turkmenistan. As Iran is a littoral state of the Caspian Sea, which is an inland sea and condominium, Kazakhstan and Russia are also Iran's direct neighbors to the north. Iran is bordered on the east by Afghanistan and Pakistan, on the south by the Persian Gulf and the Gulf of Oman, and on the west by Turkey and Iraq. Tehran is the capital, the country's largest city and the political, cultural, commercial, and industrial center of the nation. Iran is a regional power and occupies an important position in international energy security and world economy as a result of its large reserves of petroleum and natural gas.
Iran is home to one of the world's oldest continuous major civilizations, with historical and urban settlements dating back to 4000 BC. The Medes unified Iran into a kingdom in 625 BC. They were succeeded by three Iranian dynasties, the Achaemenids, Parthians and Sassanids, which governed Iran for more than 1000 years. After centuries of foreign occupation and short-lived native dynasties, Iran was once again reunified as an independent state in 1551 by the Safavid dynasty — who promoted Shia Islam as the official religion of their empire, marking one of the most important turning points in the history of Islam. Iran had been a monarchy ruled by a Shah, or emperor, almost without interruption from 1501 until the 1979 Iranian Revolution, when Iran officially became an Islamic republic on 1 April 1979.
Iran is a founding member of the UN, NAM, OIC and OPEC. The political system of Iran, based on the 1979 Constitution, comprises several intricately connected governing bodies. The highest state authority is the Supreme Leader. Shia Islam is the official religion and Persian is the official language.