Iran is home to one of the world's oldest continuous major civilizations, with historical and urban settlements dating back to 4000 BC.The southwestern part of the Iranian plateau participated in the wider Ancient Near East with Elam, from the Early Bronze Age. Hegel names the Persians as the first Historical People. The Medes unified Iran as a nation and empire in 625 BC. The Achaemenid Empire (550–330 BC), founded by Cyrus the Great, was the first of the Persian empires to rule from the Balkans to North Africa and also Central Asia, spanning three continents, from their seat of power in Persis (Persepolis). It was the largest empire one had yet seen and the first world empire.They were succeeded by the Seleucid Empire, Parthians and the Sasanians who governed Iran for almost 1,000 years, and would put Iran once again as the leading powers in the world, only this time amongst their arch rival, the Roman Empire and the successive Byzantine Empire.
The Persian Empire (Persia) proper begins in the Iron Age, following the influx of Iranian peoples. Iranian people gave rise to the Medes, the Achaemenids, the Arsacids, and the Sasanians during the classical antiquity.
Once a major empire of superpower proportions, having conquered far and wide, Iran has endured invasions too, by the Greeks, Arabs, Turks, and the Mongols. Iran has continually reasserted its national identity throughout the centuries and has developed as a distinct political and cultural entity.
The Islamic conquest of Persia (633–656) ended the Sasanians and was a turning point in Iranian history. Islamicization in Iran took place during 8th to 10th century and led to the eventual decline of the Zoroastrian religion in Persia, as well as many of its dependancies. However, the achievements of the previous Persian civilizations were not lost, but were to a great extent absorbed by the new Islamic polity and civilization.
Iran was once again reunified as an independent state in 1501 by the Safavid dynasty which established Shi'a Islam as the official religion of their empire, marking one of the most important turning points in the history of Islam.Functioning again as a leading power, this time amongst their neighboring Ottoman arch rival for centuries, 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.
In the course of the first half of the 19th century, Iran irrevocably lost many of its territories in the Caucasus which it had been ruling intermittently encompassed for millennia, comprising modern day Georgia, Dagestan, Azerbaijan, and Armenia following the Russo-Persian War (1804-1813) and Russo-Persian War (1826-1828) to its rapidly expanding and emerged neighboring rival, the Russian Empire.