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 as a nation and empire in 625 BC.
The Islamic conquest of Persia (633–656) and the end of the Sassanid Empire was a turning point in Iranian history. Iran had been a monarchy ruled by a shah, or emperor, almost without interruption from 1501 until the 1979 Islamic revolution, when Iran officially became the Islamic Republic on 1 April 1979.
Pre-Islamic
Before Iran was called Iran, and before Iranians lived there, a different group of people lived in Iran. These people were called the Elamites. The Elamites are mentioned in the Bible. The Elamites lived in a kingdom called Elam. Elam was conquered by Iranian peoples, such as the Medes (a type of Iranian), because the Elamites became weak after fighting the Assyrian people (a different people) for too long. The Iranians would then go on to conquer the Assyrians, as well.
The name Iran comes from Aryan and is also mentioned in the ancient book of the Zoroastrians, which was called the Avesta. Iran means "Aryan" in Persian. In the 19th and early 20th century, the name Aryan was used by Europeans to mean all Indo-Europeans.
Around 500 BC, present-day Iran was the center of the Persian Empire. Then, Alexander the Great took the country by fighting and the Achaemenid dynasty of Persia later ruled. After them, the Sassanian dynasty (224-651) took over.
Islamic Persia
Other people took Persia by fighting, like the Arabs (7th century), Turks (10th century) and Mongols (13th century). However, Iran has always maintained a distinct culture and continued to survive.
The Safavid dynasty (1502-1736) made Islam and Shi'a the religion of Iran although Islam was always popular then. The latest kings of Iran were from the Pahlavi Dynasty and ruled from 1925 until 1979 when there was a revolution and Ayatollah Khomeini created an Islamic republic.
In 1951, Mohammed Mossadegh was brought to power after being elected as prime minister by nearly all members of the Majlis (parliament) in Iran. His first act in office was to take control of the oil industry in Iran which had been controlled by Great Britain. Most of Britain's oil was pumped from Iran at the time. This move was seen as a danger to Great Britain's security and empire, so they tried to overthrow the government but failed. After this, they convinced the United States through diplomacy that the government of Iran was a communist threat.
The CIA worked in Iran to create riots which led to the removal of Prime Minister Mossadegh. The United States and Great Britain then made the Shah Mohammad Reza PahlaviKing of Iran, again.