Pre-Iranian era
The earliest archaeological artifacts in Iran, like those excavated at the Kashafrud and Ganj Par sites, attest to a human presence in Iran since the Lower Paleolithic era. Neanderthal artefacts dating back to the Middle Paleolithic period have been found mainly in the Zagros region at sites such as Warwasi and Yafteh Cave. Early agricultural communities began to flourish in Iran at around 8000 BC, with settlements such as Chogha Bonut, Susa and Chogha Mish developing in the Zagros region.
Dozens of pre-historic sites across the Iranian plateau point to the existence of ancient cultures and urban settlements in the fourth millennium BC, centuries before the earliest civilizations arose in nearby Mesopotamia. During the Bronze age Iran was home to several civilisations such as Elam, Jiroft and Zayandeh Rud civilisations. Elam, the most prominent of these civilisations developed in the southwest of Iran alongside those in Mesopotamia. The development of writing in Elam in 2900 BC paralleled that in Sumer. The Elamite kingdom continued its existence until the emergence of the Median and Achaemenid Empires.

Pre-Islamic statehood
During the second millenium BC proto-Iranian tribes arrived in Iran from southern Russia, rivaling the native settlers of the country. As these tribes dispersed into the wider area of Greater Iran and beyond, the boundaries of modern Iran were dominated by the Persian, Parthian and Median tribes. Soon after Zoroastrianism emerged as the main religion of the Iranian tribes.

The unification of the Median tribes under a single ruler in 728 BC led to the creation of a Median empire which by 612 BC controlled the whole of Iran as well as eastern Anatolia. A Persian revolt led by Cyrus the Great ended the Median empire in 550 BC and signaled the beginning of the Achaemenid empire. Later conquests under Cyrus and his successors expanded the empire to include Lydia, Babylon, Egypt and the lands to the west of the Indus an Oxus Rivers. Conflict on the western borders began with the famous Greco-Persian Wars which continued through the first half of the 5th century BC and ended with the Persian withdrawal from all of their European territories. The empire had a centralised, bureaucratic administration under the Emperor and a large professional army and civil services, inspiring similar developments in later empires.
In 334 BC, Alexander the Great invaded the Achaemenid Empire, defeating the last Achaemenid Emperor Darius III at the Battle of Issus in 333 BC. Following the premature death of Alexander the Great, Iran came under the control of Hellenistic Seleucid Empire. In the middle of the 2nd century BC Parthia rose to become the main power in Iran and continued as a feudal monarchy for nearly five centuries until 224 AD, when it was succeeded by the Sassanid Empire. The Sassanids established an empire roughly within the frontiers achieved by the Achaemenids, with the capital at Ctesiphon. Most of the period of the Parthian and Sassanid Empires were overshadowed by the Roman-Persian Wars, which raged on their western borders for over 700 years. These wars exhausted both Romans and Sassanids,which arguably led to the defeat of both at the hands of the invading Muslim Arabs.

Middle Ages (652–1501)
The prolonged Roman-Persian wars, as well as social conflict within the Empire opened the way for an Islamic invasion of Iran in the 7th century.[61][62] Initially defeated by the Rashidun Caliphate, Iran later came under the rule of their successors the Ummayad and Abbasid Caliphates. The process of conversion of Iranians to Islam which followed was a prolonged and gradual process. Under the new Arab elite of the Rashidun and later Ummayad Caliphates Iranians, both Muslim (mawali) and non-Muslim (Dhimmi), were discriminated, being excluded from government and military, and having to pay a special tax. In 750 the Abbasids succeeded in overthrowing the Ummayad Caliphate, mainly due to the support from dissatisfied Iranian mawali. The mawali formed the majority of the rebel army, which was led by the Iranian general Abu Muslim. After two centuries of Arab rule semi-independent and independent Iranian kingdoms (such as the Tahirids, Saffarids, Samanids and Buyids) began to appear on the fringes of the declining Abbasid Caliphate. By the Samanid era in the 9th and 10th centuries Iran's efforts to regain its independence had been well solidified.

The arrival of the Abbasid Caliphs saw a revival of Persian culture and influence, and a move away from Arabic culture. The role of the old Arab aristocracy was slowly replaced by a Persian bureaucracy. The blossoming Persian literature, philosophy, medicine, and art became major elements in the forming of a Muslim civilization during the Islamic Golden Age. The Islamic Golden Age reached its peak in the 10th and 11th centuries, during which Persia was the main theatre of scientific activity. After the 10th century, Persian, alongside Arabic, was used for scientific, philosophical, historical, mathematical, musical, and medical works, as important Iranian writers such as Nasir al-Din al-Tusi, Avicenna, Qotb al-Din Shirazi, Naser Khusraw and Biruni made contributions to Persian scientific writing.
The cultural revival that began in the Abbasid period led to a resurfacing of Iranian national identity, and so earlier attempts of Arabization never succeeded in Iran. The Iranian Shuubiyah movement became a catalyst for Iranians to regain their independence in their relations with the Arab invaders. The most notable effect of the movement was the continuation of the Persian language attested to the epic poet Ferdowsi, now regarded as the most important figure in Persian literature.
The 10th century saw a mass migration of Turkic tribes from Central Asia into the Iranian plateau. Turkic tribesmen were first used in the Abbasid army as slave-warriors (Mamluks), replacing Persian and Arab elements within the army. As a result the Mamluks gained significant political power. In 999, Iran came under the rule of Ghaznavid dynasty, whose rulers were of Mamluk Turk origin, and later under the Turkish Seljuk and Khwarezmian Empires. These Turks had been Persianised and had adopted Persian models of administration and rulership. The result of the adoption and patronage of Persian culture by Turkish rulers was the development of a distinct Turko-Persian tradition.
In 1219-21 the Khwarezmian Empire suffered a devastating invasion by Genghis Khan's Mongol army. Mongol violence and depredations killed up to three-fourths of the population of the Iranian Plateau, possibly 10 to 15 million people. Some historians have estimated that Iran's population did not again reach its pre-Mongol levels until the mid-20th century. Following the fracture of the Mongol Empire in 1256 Hulagu Khan, Genghis Khan's grandson, established the Ilkhanate dynasty in Iran. In 1370 yet another conqueror, Timur, commonly known as Tamerlane in the West, followed Hulagu's example, establishing the Timurid Dynasty which lasted for another 156 years. In 1387, Timur ordered the complete massacre of Isfahan, reportedly killing 70,000 citizens. Hulagu, Timur and their successors soon came to adopt the ways and customs of that which they had conquered, choosing to surround themselves with a culture that was distinctively Persian.

Modern era (1501–)
In 1501 Shah Ismail I re-established Iranian political unity in the form of the Safavid Dynasty. Ismail is also known for instigated a religious revolution in Iran, forcefully converting the predominantly Sunni population to the state religion of Shi'a Islam. During the Safavid era Iran once again became a centre for high civilisation and wealth, peaking under the reign of Shah Abbas I. Under his rule the state became highly centralized, the first attempts to modernize the military were made, and even a distinct style of architecture developed in his new capital at Isfahan. The Safavid era was an era of intense rivalry with the Sunni Ottoman Empire, leading to the Ottoman–Persian Wars. However, following a slow decline the Safavid dynasty was instead ended by Pashtun rebels who besieged Isfahan and defeated Soltan Hosein in 1722.
In 1729 Nader Shah successfully drove out the Pashtuns from Isfahan. By 1735 Nader Shah had regained territory lost to the Ottomon and Russian Empires, and in 1738 staged a very profitable incursion into the Mughal Empire. His military successes on all fronts earned him the nickname "Napoleon of Persia" or "the second Alexander". Following a brief civil war sparked by Nader Shah's assassination Karim Khan came to power, giving himself the title Vakil e-Ra'aayaa (Representative of the People), bringing a period of relative peace and prosperity.
Another civil war ensued Karim Khan's death in 1779, out of which Aga Muhammad Khan emerged victorious, founding the Qajar Dynasty in 1794 and establishing Tehran as his capital. Qajar rulership was marked by its inadequate response to change and its failure to maintain Iranian territorial integrity and sovereignty, and is consequently characterised by over a century of misrule. The Great Persian Famine of 1870–1871 is believed to have caused the death of 1.5 million persons, or 20–25% of Persia's population. Whilst resisting efforts to be colonised, Iran suffered as a result of The Great Game, losing much of its territory in the Russo-Persian and the Anglo-Persian Wars. A series of protests took place in response to the sale of concessions to foreigners by Nasser al-Din Shah and Mozaffar ad-Din Shah between 1872 and 1905, the last of which resulted in the Iranian Constitutional Revolution and establishment of Iran's first national parliament (majles) in 1906. However, Mozaffar ad-Din Shah's son Mohammad Ali Shah wished to recover the power lost by his father, and so rescinded the constitution, bombed the majles building and abolished parliament in 1908. The struggle continued until 1911 when Mohammad Ali's forces were finally defeated.
In 1925 Reza Khan, Prime Minister of Iran and former general of the Persian Cossack Brigade, overthrew the weakening Qajar Dynasty and became Shah.
In 1964 Imam Khomeini (RA) _whom was arrested and imprisoned for 18 months_ publicly criticized the United States government. The Shah was persuaded to send him into exile by General Hassan Pakravan. Imam Khomeini (RA) was sent first to Turkey, then to Iraq and finally to France. While in exile, he continued to denounce the Shah.

Islamic revolution
The Iranian Revolution, also known as the Islamic Revolution, began in January 1978 with the first major demonstrations against the Shah. After strikes and demonstrations, the Shah fled the country in January 1979 and Ayatollah Ruhollah Khomeini (RA) returned from exile to Tehran. The Pahlavi dynasty collapsed ten days later, on 11 February, when Iran's military declared itself "neutral" after guerrillas and rebel troops overwhelmed troops loyal to the Shah in armed street fighting. Iran officially became an Islamic Republic on 1 April 1979, when Iranians overwhelmingly approved a national referendum to make it so.

In December 1979, the country approved a theocratic constitution, whereby Imam Khomeini (RA) became Supreme Leader of the country. The speed and success of the revolution surprised many throughout the world, as it had not been precipitated by a military defeat, a financial crisis, or a peasant rebellion. Although both nationalists and Marxists joined with Islamic traditionalists to overthrow the Shah, and the revolution ultimately resulted in an Islamic Republic under Ayatollah Ruhollah Khomeini (RA).
Iran – United States relations deteriorated rapidly during the revolution. On 4 November 1979, a group of Iranian students seized US embassy personnel, as it became the embassy of "den of spies".

War
Iraqi leader Saddam Hussein decided to take advantage of what he perceived to be disorder in the wake of the Iranian Revolution and its unpopularity with Western governments. The once-strong Iranian military had been disbanded during the revolution. Saddam sought to expand Iraq's access to the Persian Gulf by acquiring territories that Iraq had claimed earlier from Iran during the Shah's rule. On 22 September 1980 the Iraqi army invaded Iran at Khuzestan, precipitating the Iran–Iraq War.

Construction era, after war
Following the Iran–Iraq War President Akbar Hashemi Rafsanjani and his administration concentrated on a pragmatic pro-business policy of rebuilding and strengthening the economy. Rafsanjani served until 1997 when he was succeeded by the Mohammad Khatami.
In the 2005 presidential elections, Iran made yet another change in political direction, when Mahmoud Ahmadinejad was elected over Akbar Hashemi Rafsanjani. In 2009 Iranian presidential election on 12 June 2009, the tenth presidential election hold and again Dr. Ahmadinejad was elected as the Iranian president.