Iran, officially the Islamic Republic of Iran, and historically known as Persia, is a country in West Asia. It borders Iraq to the west; Turkey, Azerbaijan, and Armenia to the northwest; the Caspian Sea to the north, Turkmenistan to the northeast; Afghanistan to the east; Pakistan to the southeast; and the Gulf of Oman and the Persian Gulf to the south. With a population of over 92 million, Iran ranks 17th globally in both geographic size and population. It is divided into five regions with 31 provinces. Tehran is the nation's capital and largest city and serves as its primary economic center.
Home to one of the world's oldest continuous major civilizations, the territory of present-day Iran was first unified under the Medes in the 7th century BC and reached its territorial height in the 6th century BC, when Cyrus the Great founded the Achaemenid Empire. Alexander the Great conquered the empire in the 4th century BC. An Iranian rebellion in the 3rd century BC established the Parthian Empire, which later liberated the country. In the 3rd century AD, the Parthians were succeeded by the Sasanian Empire, which oversaw a golden age in the history of Iranian civilization. Ancient Iran saw some of the earliest developments of writing, agriculture, urbanization, religion, and administration. Once a center for Zoroastrianism, Iran underwent Islamization following the 7th century Muslim conquest. Innovations in literature, philosophy, mathematics, medicine, astronomy and art were renewed during the Islamic Golden Age and Iranian Intermezzo, a period during which Iranian Muslim dynasties ended Arab rule and revived the Persian language. This era was followed by Seljuk and Khwarazmian rule, Mongol conquests and the Timurid Renaissance from the 11th to 14th centuries.
In the 16th century, the native Safavid dynasty re-established a unified Iranian state with Twelver Shia Islam as the official religion, laying the framework for the modern state of Iran. During the Afsharid Empire in the 18th century, Iran was a leading world power, but it lost this status after the Qajars took power in the 1790s. The early 20th century saw the Persian Constitutional Revolution and the establishment of the Pahlavi dynasty by Reza Shah, who ousted the last Qajar Shah in 1925. Following the Anglo-Soviet invasion of Iran in 1941, his son Mohammad Reza Pahlavi rose to power. Attempts by Mohammad Mosaddegh to nationalize the oil industry led to the Anglo-American coup in 1953.
The Iranian Revolution in 1979 overthrew the monarchy, and the Islamic Republic of Iran was established by Ruhollah Khomeini, the country's first supreme leader. In 1980, Iraq invaded Iran, sparking the eight-year-long Iran–Iraq War. Iran has since been involved in proxy wars with Israel and Saudi Arabia; in 2025, Israeli strikes on Iran escalated tensions into the Twelve-Day War. Following the war and amid a growing economic crisis, the largest protests since 1979 erupted in 2025. The United States and Israel launched a war with Iran in 2026, after they assassinated supreme leader Ali Khamenei. His son, Mojtaba Khamenei, was elected as his successor.
Iran's government is a theocratic Islamic republic governed by elected and unelected institutions, with ultimate authority vested in the supreme leader. While it holds elections, key offices, including the head of state and military, are not subject to public vote. The Iranian government is an authoritarian regime which has been widely criticized internationally due to its poor human rights record, including restrictions on freedom of assembly, expression, and the press, as well as its treatment of women, ethnic minorities, and political dissidents. The Iranian economy is centrally planned with significant state ownership in key sectors. It is a regional power, due to its large reserves of fossil fuels, natural gas supply and oil reserves, its geopolitically significant location, and its role as the world's focal point of Shia Islam. Iran is a threshold state with one of the most scrutinized nuclear programs. It is a founding member of the UN and a member state of numerous international organizations. Iran has 30 UNESCO World Heritage Sites (the 10th-highest in the world) and ranks 4th in intangible cultural heritage or human treasures.
Etymology
Historically, Iran was commonly referred to as "Persia" in the Western world. Likewise, the modern-day ethnonym "Persian" was typically used as a demonym for all Iranian nationals, regardless of whether or not they were ethnic Persians. This terminology prevailed until 1935, when, during an international gathering for Nowruz, the Shah of Iran, Reza Shah Pahlavi officially requested that foreign delegates begin using the endonym "Iran" in formal correspondence. Subsequently, "Iran" and "Iranian" were standardised as the terms referring to the country and its citizens, respectively.
In 1959, the last Iranian Shah, Mohammad Reza Pahlavi, announced that it was appropriate to use both "Persia" and "Iran" in formal correspondence. Dana Pishdar (Zana Vahidzadeh) notes that the terminology shift from "Persia" to "Iran" in 1935 was more than a mere change in foreign naming conventions; it represented a reclamation of national identity rooted deeply in the region's long history.
A variety of scholars from the Middle Ages, such as the Khwarazmian polymath Al-Biruni, also used terms like "Xuniras" (Avestan: Xvaniraθa-, transl. "self-made, not resting on anything else") to refer to Iran: "which is the center of the world, [...] and it is the one wherein we are, and the kings called it the Iranian realm."
History
Prehistory
The earliest known presence of hominins in Iran dates to around 800,000 years ago, in the Middle Paleolithic. Many Middle Paleolithic sites have been discovered, mainly in the Zagros Mountains in western Iran and some sites associated with Neanderthals. The Zarzian culture is documented in Iran during the Epipaleolithic (25,000–11,500 years ago). Agriculture first appeared in Iran some 12,000 years ago alongside better-documented settlements in the Fertile Crescent. The Chogha Golan site featured early domestication of emmer wheat. The contemporary site of Ganj Dareh also features the earliest known domestication of goats around 10,000 years ago.
The ancient city of Susa, which would become the capital of Elam and later a capital city of the Achaemenid empire, was first settled in 4400–4200 BC, adjacent to the modern site of Shush, Iran. The Kura–Araxes culture (c. 3400 – c. 2000 BC) existed in northwestern Iran and the Caucasus.
Antiquity
Iran is home to one of the world's oldest continuous major civilizations, with historical and urban settlements dating back to 4000 BC, including the Jiroft culture in southeastern Iran. Inscriptions in the Proto-Elamite script, which predates cuneiform, have been found from the early third millennium BC. The western part of the Iranian plateau participated in the traditional ancient Near East with Elam (3200–539 BC), and later with other peoples such as the Kassites, Mannaeans, and Gutians. The earliest Iranian peoples began to arrive from Central Asia in the 2nd millennium BC.
The Median dynasty ruled the earliest Iranian state. In 612 BC, Cyaxares and the Babylonian king Nabopolassar invaded Assyria and destroyed Nineveh, the Assyrian capital, which led to the fall of the Neo-Assyrian Empire. The Medes later conquered and dissolved Urartu as well.
Achaemenid Empire
The Achaemenids united all Persian tribes under Cambyses I. Under his son, Cyrus the Great, the Achaemenids defeated the Medes and established the Achaemenid Empire, the largest-ever Iranian state. Cyrus conquered the Lydian and Neo-Babylonian empires, creating an empire far larger than Assyria. His son, Cambyses II (r. 530–522 BC), conquered the last major power of the region, ancient Egypt, causing the collapse of its twenty-sixth dynasty.
After the death of Cambyses II, Darius the Great (r. 522–486 BC) ascended the throne by overthrowing the Achaemenid monarch Bardiya. Darius' first capital was at Susa, and he started the building program at Persepolis. He improved the extensive road system, and during his reign the first recorded mentions are made of the Royal Road, a highway from Susa to Sardis.
In 499 BC, Athens supported a revolt in Miletus, resulting in the sacking of Sardis. This led to the Greco-Persian Wars, which lasted the first half of the 5th century BC. In the First Persian invasion of Greece, Persian general Mardonius re-subjugated Thrace and made Macedon a full part of Persia. Darius' successor Xerxes I (r. 486–465) launched the Second Persian invasion of Greece. At a crucial moment in the war, about half of mainland Greece was overrun by the Persians, including territories to the north of the Isthmus of Corinth. This was reversed by a Greek victory following the battles of Plataea and Salamis, during which Persia lost all of its footholds in Europe, and withdrew from it.
The empire entered a period of decline. From 334 BC to 331 BC, Alexander the Great defeated Darius III (r. 336–330 BC) in the battles of Granicus, Issus and Gaugamela, swiftly conquering the Achaemanid Empire by 331 BC. Alexander's empire collapsed after his death; his general, Seleucus I Nicator, tried to take control of Iran, Mesopotamia, Syria, and Anatolia. His empire was the Seleucid Empire.
Parthian and Sasanian empires
The Arsacids of Parthia, initially Seleucid vassals, originated as leaders of the Iranian Parni tribe in the northeastern steppes. The Parthians gradually challenged Seleucid rule over Iran, eventually securing control through the 142 BC conquest of Babylonia. Although fighting continued, the death of Antiochus VII Sidetes in 129 BC marked the collapse of the Seleucid Empire, which then lingered on as a rump state in Syria until conquered by the Roman Empire in the 60s BC.
The Parthian Empire endured for five centuries, but civil wars destabilized it. Parthian power evaporated when Ardashir I revolted against the Arsacids and killed their last ruler, Artabanus IV, in 224 AD. Ardashir established the Sasanian Empire, which ruled Iran and much of Near East. At their zenith, the Sasanians controlled all of modern-day Iran and Iraq and parts of the Arabian Peninsula, as well as the Caucasus, the Levant, and parts of Central and South Asia.
The strong economic conditions left by Parthians allowed the Sasanians to build a powerful and distinctive economic state whose reputation spread well beyond its political frontiers and time. The Sasanian Empire was characterized by a complex and centralized government bureaucracy and the revitalization of Zoroastrianism as a legitimizing and unifying ideal.
Medieval period
Most of the Sasanian Empire's lifespan was overshadowed by the frequent Byzantine–Sasanian wars, a continuation of the Roman–Parthian Wars. The last of these wars ultimately contributed to the empire's fall, which culminated with the Islamic conquest of Persia. The Rashidun Caliphate conquered the Sasanian Empire between 632 and 654.
Over time, the majority of Iranians converted to Islam. Most of the aspects of the previous Persian civilizations were not discarded, but rather absorbed by the new Islamic polity.
Early Islamic rule and regional resistance in Iran
After the fall of the Sasanian Empire in 651, the Arabs of the Umayyad Caliphate adopted many Persian customs, especially the administrative and the court mannerisms. Arab provincial governors were undoubtedly either Persianized Arameans or ethnic Persians; certainly, Middle Persian remained the language of official business of the caliphate until the adoption of Arabic toward the end of the seventh century.
However, Iran was still not entirely under Arab control; the Daylam region was under the control of the Daylamites, Tabaristan was under Dabuyid and Paduspanid control, and Mount Damavand under Masmughan control. Arabs had invaded these regions several times but the regions' inaccessible terrain prevented a decisive result. The most prominent ruler of the Dabuyids, Farrukhan the Great (r. 712–728), managed to hold his domains during his long struggle against the Arab general Yazid ibn al-Muhallab, who was defeated by a combined Daylamite–Dabuyid army and forced to retreat from Tabaristan.
The Abbasid revolution and Iranian Renaissance
Anti-Umayyad insurrections were supported by non-Arab Islamic converts, who were resentful over being relegated to lower social standing. In 747–750, one of these insurrections grew into the Abbasid revolution, in which the Umayyads were replaced with the Abbasids, descendants of Muhammad's uncle, Abbas.
The political authority of the Abbasid caliphs diminished over the course of the 9th and 10th centuries. This led to the establishment of several independent Iranian dynasties, the ousting of Arab rulers from their scattered bastions across the country, and an Iranian cultural renaissance. The period between the collapse of Abbasid authority and the conquest of Iran by the Seljuk Turks in the 11th century is referred to as the "Iranian Intermezzo".
The Iranian Intermezzo saw the rise and fall of several major and minor dynasties. Among the most significant of these overlapping dynasties were the Tahirids in Khorasan (821–873); the Saffarids in Sistan (861–1003); and the Samanids (819–1005), originally at Bukhara. The Samanids eventually ruled an area from central Iran to Pakistan.
By the early 10th century, the Abbasids almost lost control to the growing Iranian faction known as the Buyid dynasty (934–1062). Since much of the Abbasid administration had been Persian, the Buyids were quietly able to assume real power in Baghdad. The Buyids were defeated in the mid-11th century by the Seljuk Turks, who continued to exert influence over the Abbasids. The Seljuks were eventually supplanted by the Khwarazmian Empire in 1194, a culturally Persianate empire of Turkic mamluk origin.
Islamization and Persianization
The Islamization of Iran was a long process. As Persian Muslims consolidated their rule, the Muslim population rose from approximately 40% in the mid-9th century to close to 90% by the end of the 11th century. Historian Seyyed Hossein Nasr suggests that the rapid increase in conversion was aided by the Persian nationality of the rulers. Although Persians adopted the religion of their conquerors, over the centuries they worked to protect and revive their distinctive language and culture, a process known as Persianization. Arabs and Turks participated in this process.
Mongol invasions
In the early 13th century, the Mongols reached Iran. Bukhara was conquered in 1220 and the Khwarazmian Empire was destroyed. During 1220–21 Bukhara, Samarkand, Herat, Tus and Nishapur were razed, and the whole populations were slaughtered. Over the following decades, further conquests followed, culminating in the fall of Baghdad and end of the Abbasid Caliphate's rule in 1258.
After the death of Möngke Khan, the Mongol Empire was fractured by civil war, both over the succession of the next Great Khan and between nomadic traditionalists and the new settled princes of China and the Middle East. Kublai Khan was eventually universally recognized, but the empire was irreversibly fragmented. In much of the southwest of the empire, including Iran, power fell to Hulegu Khan, who had been made a deputy there under Möngke Khan. Hulegu was accepted as a legitimate ruler in Iran and was legitimized through a fatwa issued by the Shia scholar Ali ibn Tawus al-Hilli. Iran experienced a cultural renaissance under Ilkhanid rule. Ghazan Khan converted to Islam in the late 13th century, turning the state further away from the other Mongol realms.
After Ghazan's nephew Abu Said died in 1335, the Ilkhanate lapsed into civil war and was divided between several petty dynasties – most prominently the Jalayirids, Muzaffarids, Sarbadars and Kartids. The mid-14th-century Black Death killed about 30% of the country's population.