<P> The Oxford English Dictionary traces the use of the phrase satellite state in English back at least as far as 1916 . </P> <P> In times of war or political tension, satellite states sometimes serve as buffers between an enemy country and the nation exerting control over the satellites . "Satellite state" is one of several contentious terms used to describe the (alleged) subordination of one state to another . Other such terms include puppet state and neo-colony . In general, the term "satellite state" implies deep ideological and military allegiance to the hegemonic power, whereas "puppet state" implies political and military dependence, and "neo-colony" implies (often abject) economic dependence . Depending on which aspect of dependence is being emphasised, a state may fall into more than one category . </P> <P> When the Mongolian Revolution of 1921 broke out, Mongolian revolutionaries expelled Russian White Guards (during the Russian Civil War of 1917--1923 following the Communist October Revolution of 1917) from Mongolia, which became independent when the Qing dynasty collapsed in 1911, with the assistance of the Soviet Red Army . The revolution also officially ended Manchurian sovereignty over Mongolia, which had existed since 1691 . Although the theocratic Bogd Khaanate of Mongolia still nominally continued, with successive series of violent struggles, Soviet influence got ever stronger, and after the death of the Bogd Khaan ("Great Khan", or "Emperor"), the Mongolian People's Republic was proclaimed on November 26, 1924 . A nominally independent and sovereign country, it has been described as being a satellite state of the Soviet Union in the years from 1924 until 1990 . </P> <P> During the Russian Civil War, the Soviet Red Army troops took Tuva in January 1920, which had also been part of the Qing Empire of China and a protectorate of Imperial Russia . The Tuvan People's Republic, was proclaimed independent in 1921 and was a satellite state of Soviet Union until its annexation in 1944 by the Soviet Union . </P>

By what means were the satellite states kept under control by the soviets