Mongolia had gained "de facto" independence from the Republic of China in the Mongolian Revolution of 1921. In that year the last Chinese troops in the country had been expelled by the White Russian general Roman von Ungern-Sternberg, prompting Soviet intervention. The Mongolian People's Republic was effectively an unrecognized satellite state of the Soviet Union (USSR). Towards the end of World War II, the USSR pushed China for formal recognition of the "status quo", threatening to stir up Mongolian nationalism within China. In the Sino-Soviet Treaty of Friendship and Alliance signed on 14 August 1945, China agreed to recognize Mongolian independence after a successful referendum. The actual referendum was regarded by both sides as political theatre.