The First inhabitants of Iran history were living in western Asia. But by arriving Aryans who are known as Indo-Europeans today, they gradually started mingling with the old native Asians. There is a belief which is mentioned that Aryans were the ancestors of the people of present India, Iran, and most of Western Europe.
Until two main Indo-European tribes moving into south of Iran, it was at first the Medes who play the dominant role. They established their capital at Ecbatana (Hamedan in today) as powerful as Assyria. In 612 they combine with Babylon to conquer the Assyrian capital at Nineveh. Until the Persian king Cyrus the Great overthrew the Medes and became ruler of the Achaemenid (Persian) Empire, which reached from the Indus to the Nile at its zenith in 525 B.C.Cyrus the Great was the founder of the empire and he is the first to establish the order of human rights. In this period Iran stretched from the Aegean coast of Asia Minor to Afghanistan, as well as south to Egypt. The mentioned dynasty was extinct by Alexander the Great invasion to Iran. Then, the Empire of Iran was followed by The Seleucid Greek Dynasty.
After the Seleucids, Iran witnesses about dozen successive dynasties reigning over itself, Dynasties such as Parthian, Sassanid, Samanid, Ghaznavid, Safavid, Zand, Afsharid, Qajar and Pahlavi.(Iran History)
Arab Muslims and Mongols were among other conquerors who have attacked Iran after Alexander the Great. After the Arab’s attack, Persians, who were the followers of Zoroaster, gradually converted to Islam and it was in Safavid period when Shiite Islam became the official religion of Iran. Also subsequent conquests by Afghans and Qājār Turks had the same result. Since Qajar dynasty on, due to the incapability of the rulers, Iran intensely gets smaller and smaller. In this time, the Russians and the Britains fought for economic control of the area, and during the World War I, Iran’s neutrality did not stop it from becoming a battlefield for Russian and British troops.
In 1921 Reza Khan led a group of soldiers into Tehran. He demanded that the cabinet be deactivated and that the failing Qajar shah appoint him as a commander of the military. The Qajar dynasty, which had ruled Iran since 1785, was deposed in 1925. Shortly thereafter, Reza Khan has been assigned as the Shah and established the Pahlavi Dynasty.
In 1979, the nation, under the leadership of Ayatollah Khomeini, erupted into revolution and the current Islamic republic of Iran was founded.