Iran

The territory of present-day Iran has been continuously inhabited since the Paleolithic period and hosted some of the earliest urban civilisations of the ancient Near East. The Elamite kingdom, centred on Susa in the southwest, flourished from the late fourth millennium BCE and remained a significant power for more than two millennia. From the second millennium BCE, Iranian-speaking peoples, including the Medes and Persians, migrated onto the plateau. The Median confederation, consolidated in the seventh century BCE, gave way in 550 BCE to Cyrus the Great, founder of the Achaemenid Empire, which at its height stretched from the Indus Valley to the Aegean and from the Caucasus to Egypt. Following Alexander of Macedon's conquest in 330 BCE, the region passed through the Seleucid and Parthian periods before the Sasanian dynasty (224 to 651 CE) restored a centralised Persian state, codified Zoroastrianism as the state religion, and contested Late Antiquity with the Roman and Byzantine empires.

The Arab conquest of the mid-seventh century brought Islam to Iran and integrated the plateau into the early caliphates, though Persian language, administration, and literary culture re-emerged forcefully under regional dynasties such as the Samanids, Buyids, and Ghaznavids. Successive waves of Turkic and Mongol invasions, most notably the Seljuks in the eleventh century and the Ilkhanate established after Hulagu's sack of Baghdad in 1258, reshaped the political map. The Timurid revival of the fourteenth and fifteenth centuries was followed in 1501 by the Safavid dynasty under Shah Ismail I, who imposed Twelver Shia Islam as the state confession, an act that durably defined Iran's religious identity. The Safavids were succeeded after a turbulent interregnum by the Afsharids, the Zands, and ultimately the Qajars, who ruled from 1789 and presided over significant territorial losses to the expanding Russian Empire under the treaties of Gulistan (1813) and Turkmenchay (1828).

Pressure from Russia and Britain, combined with internal demands for reform, produced the Constitutional Revolution of 1905 to 1911, which established a parliament, the Majles, and curbed royal authority. In 1925, Reza Khan deposed the last Qajar shah and founded the Pahlavi dynasty, embarking on a programme of centralisation, secular modernisation, and infrastructure building. Allied forces occupied Iran during the Second World War and compelled his abdication in 1941 in favour of his son, Mohammad Reza Pahlavi. The 1953 coup, organised with American and British involvement, removed the elected prime minister Mohammad Mossadegh after his nationalisation of the oil industry and consolidated the shah's rule. Accelerated modernisation under the White Revolution of the 1960s brought social change but also widespread political opposition.

The Islamic Revolution of 1979 ended the monarchy and established the Islamic Republic of Iran under Ayatollah Ruhollah Khomeini, ratified by referendum that year. The new state was tested almost immediately by the Iran, Iraq War (1980 to 1988), which inflicted heavy casualties and economic damage. In subsequent decades Iran navigated reformist and conservative cycles in elected politics, sustained tensions with Western states over its nuclear programme, and pursued an extensive regional foreign policy. The 2015 Joint Comprehensive Plan of Action lifted some sanctions before its partial unraveling after 2018.

Iran today is a unitary Islamic republic that combines elected institutions, including a directly elected president and the Majles, with appointed clerical bodies; ultimate constitutional authority rests with the Supreme Leader, currently Ayatollah Ali Khamenei.