Iran is a cradle of human civilization. In the late 4th and early 3rd millennium B.C. Elamite civilization rose on the lowland Khuzestan, in the South-west of Iran. In the late 2nd millennium B.C. the Iranians migrating southward from the Central Asian Steppes began to settle in the Iranian plateau. By the mid-9th century B.C. two major groups of Iranians rose to be the dominant force on the plateau: the Medes and the Persians. In 550 B.C., the Persians defeated the Medes, and the Achaemenid kings appeared on the international scene. The Parthian and Sassanian dynasties ruled Iran successively. In 625 the Sassanians were defeated by the Muslim armies and the vast majority of Iranians converted to Islam, attracted by the divine teachings of this religion.
After the Arab invasion of Iran, the Saffarids were the first independent Iranian Muslim dynasty established in Iran (866-903). The Samanids and the Buyids also made great attempts to bring to fruition the Iranian Renaissance. In 1216 the Mongols, sweeping in with relentless fury, obliterated many Iranian cities.
In the Safavid period (1501-1736) when Iran gained a powerful dynasty, the country made great progress. The Afsharids and Zands were the next dynasties that ruled Iran successively in the 18th century. The 19th century, when the Qajars reigned over Iran, was a time of disintegration for the country. Many events, both internal and external, caused it to fall into decay. In 1925, after the deposition of the last Qajar shah, Reza Khan transferred sovereignty to himself.
In the reign of Reza Shah and his son, Mohammad Reza Pahlavi, the increasing political and economical dependence on the western countries as well as disrespect to religious values raised hatred of people for the Pahlavi regime. This hatred was manifested in demonstrations against the government under the leadership of Ayatollah Khomeini in 1978, leading to the establishment of the Islamic Republic of Iran in 1979.