The Anglo-Soviet invasion of Iran or Anglo-Soviet invasion of Persia was the joint invasion of the neutral Imperial State of Iran by the United Kingdom and the Soviet Union in August 1941. The invasion, code name Operation Countenance, was largely unopposed by the numerically and technologically outmatched Iranian forces. The multi-pronged coordinated invasion took place along Iran's borders with the Kingdom of Iraq, Azerbaijan SSR, and Turkmen SSR, with fighting beginning on 25 August and ending on 31 August when the Iranian government formally agreed to surrender, having already agreed to a ceasefire on 30 August.The invasion took place two months after the Axis invasion of the Soviet Union and the Soviet Union's subsequent alliance with the United Kingdom. The attack also took place less than two months after Allied victories over pro-Axis forces in neighbouring Iraq and French Syria and Lebanon.

The invasion's strategic purpose was to ensure the safety of Allied supply lines to the USSR (see the Persian Corridor), secure Iranian oil fields, limit German influence in Iran (Reza Shah was considered friendly to Nazi Germany) and preempt a possible Axis advance from Turkey through Iran toward the Baku oil fields or British India. Following the invasion, on 16 September 1941 Reza Shah abdicated and was forced into exile by the invading British. He was replaced by his young son Mohammad Reza Pahlavi.

Tehran (; Persian: تهران Tehrān [tehˈɾɒːn] (listen)) is the capital of Iran and Tehran Province. With a population of around 8.7 million in the city and 15 million in the larger metropolitan area of Greater Tehran, Tehran is the most populous city in Iran and Western Asia, and has the second-largest metropolitan area in the Middle East, after Cairo. It is ranked 24th in the world by metropolitan area population. It is also known for its sprawling development and futuristic architecture, epitomized by the Milad Tower and the Fereshteh Pasargad Hotel, designed by Zaha Hadid.In the Classical era, part of the territory of present-day Tehran was occupied by Rhages, a prominent Median city destroyed in the medieval Arab, Turkic, and Mongol invasions. Modern Ray is urban area absorbed into the metropolitan area of Greater Tehran.

Tehran was first chosen as the capital of Iran by Agha Mohammad Khan of the Qajar dynasty in 1786, because of its proximity to Iran's territories in the Caucasus, then separated from Iran in the Russo-Iranian Wars, to avoid the vying factions of the previously ruling Iranian dynasties. The capital has been moved several times throughout history, and Tehran is the 32nd national capital of Persia. Large-scale demolition and rebuilding began in the 1920s, and Tehran has been a destination for mass migrations from all over Iran since the 20th century.Tehran is home to many historical locations, including the royal complexes of Golestan, Sa'dabad, and Niavaran, where the two last dynasties of the former Imperial State of Iran were seated. Tehran's most famous landmarks include the Azadi Tower, a memorial built under the reign of Mohammad Reza Shah of the Pahlavi dynasty in 1971 to mark the 2,500th anniversary of the founding of the Imperial State of Iran, and the Milad Tower, the world's sixth-tallest self-supporting tower, completed in 2007, and the Tabiat Bridge, completed in 2014.Most of the population are Persian, and roughly 99% of them understand and speak the Persian language, but large populations of other ethno-linguistic groups live in Tehran and speak Persian as a second language.Tehran has an international airport (Imam Khomeini Airport), a domestic airport (Mehrabad Airport), a central railway station, a rapid transit system, Tehran Metro, a bus rapid transit system, trolleybuses, and a large network of highways.

Plans to relocate Iran's capital from Tehran to another area, due to air pollution and earthquakes, have so far not yet received approval. A 2016 survey of 230 cities by consultant Mercer ranked Tehran 203rd for quality of life. According to the Global Destinations Cities Index in 2016, Tehran is among the top ten fastest growing destinations.The City Council declared October 6 Tehran Day in 2016, celebrating the day in 1907 when the city officially became the capital of Iran.