The British considered Persia—modern-day Iran—to be a strategically important asset. As well as its vast oil reserves, the country also provided the British with a vital land passage to the eastern half of its empire. It was considered important, then, for the British to have a pliable government in Tehran on whom they could rely.

Unfortunately for the British, the ruling Qajars were unable to provide such a government. Weak and incompetent, the Qajars lacked the necessary resolve to face down the threat from Soviet-backed insurgents.

Like the British, the Soviets also had strategic designs on Persia and were keen to establish greater influence there. They did this by helping to set up a short-lived People's Republic in the city of Rasht. A guerrilla force, augmented by regular units of the Red Army, prepared to march on Persia's capital city, Tehran, thus generating a considerable political crisis.

Perturbed by this dangerous turn of events, the British engineered a coup that effectively removed the Qajars from power. They organized an insurgent force of 3,000–4,000 troops under the command of Reza Khan, Brigadier-General of the Persian Cossack Brigade. Once inside Tehran, Reza Khan and his men met with little resistance and the coup was a success.

For the next four years, Reza Khan set about securing Persia's borders and dealing with internal enemies. In 1925, he was made king, or Shah, of Persia, and his dynasty, the Pahlavis, would rule the country for the next fifty-four years with Western support.