Who pushed the British out of Persia in the 1920s?

During World War I, Persia generally did not take part in the war, but was used as a battle ground of the Soviets and Ottoman Turkish forces. The British also occupied the southern Persian region, expanding their interest in Persia. In 1920-1921, the Soviets invaded northern Persia. Tensions grew in the 1940s during the Anglo-Soviet invasion of Persia.