Starosselsky, whom Reza Shah had helped, in 1918, take over the brigade. In November 1919, he chose the last name Pahlavi for himself, which later became the name of the dynasty he founded. Rise to power 1921 coup In the aftermath of the Russian Revolution, Persia had become a battleground. In 1917, Britain used Iran as the springboard for the launching of an expedition into Russia as part of their intervention in the Russian Civil War on the side of the White movement. The Soviet Union responded by annexing portions of northern Persia, creating the Persian Socialist Soviet Republic. The Soviets extracted ever more humiliating concessions from the Qajar government, whose ministers Ahmad Shah was often unable to control. By 1920, the government had lost virtually all power outside its capital: British and Soviet forces exercised control over most of the Iranian mainland. In late 1920, the Soviets in Rasht prepared to march on Tehran with "a guerrilla force of 1,500 Jangalis, Kurds, Armenians, and Azerbaijanis", reinforced by the Soviet Red Army. This, along with various other unrest in the country, created "an acute political crisis in the capital." On 14 January 1921, the commander of the British Forces in Iran, General Edmund "Tiny" Ironside, promoted Reza Khan, who had been leading the Tabriz battalion, to lead the entire brigade. About a month later, under British direction, Reza Khan led his 3,000-4,000 strong detachment of the Cossack Brigade, based in Niyarak, Qazvin, and Hamadan, to Tehran and seized the capital. He forced the dissolution of the previous government and demanded that Zia ol Din Tabatabaee be appointed Prime Minister. Reza Khan's first role in the new government was as commander of the Iranian Army, which he combined with the post of Minister of War. He took the title Sardar Sepah (), or Commander-in-Chief of the Army, by which he was known until he became Shah. While Reza Khan and his Cossack brigade secured Tehran, the Persian envoy in Moscow negotiated a treaty with the Bolsheviks for the removal of Soviet troops from Persia. Article IV of the Russo-Persian Treaty of Friendship allowed the Soviets to invade and occupy Persia, should they believe foreign troops were using it as a staging area for an invasion of Soviet territory. As Soviets interpreted the treaty, they could invade if events in Persia should prove threatening to Soviet national security. This treaty would cause