As World War II intensified, the United Kingdom and the Soviet Union were increasingly concerned about the political situation in Iran. Mohammad Reza Pahlavi, the Shah of Iran, was perceived to have ties with Nazi Germany, which posed a significant threat to the Allies' interests in the region. To mitigate this risk, both nations decided to jointly invade Iran. The operation, known as Operation Countenance, commenced on August 25, 1941. British forces commenced their advance from the south, moving toward the oil-rich city of Abadan, while Soviet troops moved in from the north, crossing the Iranian borders near Soviet Armenia.

The invasion was characterized by its speed and efficiency, as the Allies faced minimal resistance from the Iranian military, which was ill-equipped and poorly prepared. Within a few weeks, major Iranian cities, including Tehran, were under Allied control. The occupation aimed not only to secure oil supplies but also to maintain a supply route to the Soviet Union through Iran, crucial for the war effort against Germany. Subsequently, Iran was forced to accept foreign guarantees of neutrality, effectively ending any pro-German ambitions within the country.

In the months following the invasion, the Allies established a new Iranian government, which ultimately led to political changes in the country. Despite the occupation, some Iranian citizens saw the intervention as a means to rid the nation of foreign influence, leading to a complex legacy of anti-Western sentiment that would evolve in subsequent decades.