What role did the Soviet Union play in the rise and fall of the communism in eastern europe?

Please answer HW..due tomarrow

.....These political and social changes, though, were overshadowed by the desperate struggle for survival in which the Communist regime soon found itself, and which in the process transformed it. Lenin believed, like Marx and Engels before him, that a communist government could survive in Russia only if it sparked socialist revolutions in the advanced capitalist societies of Western and central Europe. In the afterglow of 1917, this seemed attainable, as left-wing insurrections flared in Finland, Germany, Hungary, and several other countries. Lenin did what he could to help. In 1919 the Soviet government sponsored the formation of the Communist International, or Comintern, which promoted world revolution (International: The Third International). The Comintern instructed its members to split away from reformist socialist parties in their host countries and set up revolutionary parties modeled on the Communist Party and faithful to Moscow. But working-class uprisings outside of Russia were short-lived and ultimately failed. No country, with the exception of landlocked Mongolia, emulated Russia’s example, confirming its isolation among hostile capitalist societies......
Stalin’s foreign policy centered on securing the borders of the Soviet state and, when an opportunity presented itself, expanding the state’s influence. He converted the Comintern into a pliant tool of Soviet policy. Like the domestic bureaucracy, it was mercilessly purged in the 1930s of anyone not fully obedient to Stalin’s will. One of the Comintern’s most difficult assignments was to propagandize the twists and turns of the Soviet party line. For most of the 1920s, the Comintern pressured foreign communists to go it alone politically. Then, in the mid-1930s, it encouraged “popular front” alliances with social democrats and liberals against right-wing and fascistic parties. In 1939, upon conclusion of an alliance with Nazi Germany (see German-Soviet Nonaggression Pact), this edict was reversed—only to be reinstated in 1941 when the Nazis’ invasion brought the Soviet Union into World War II as an ally of the Western powers. In 1943 Stalin ordered the Comintern disbanded, concerned that it would inhibit wartime collaboration with the Allies. In 1947 he instituted the Cominform (Communist Information Bureau), consisting only of the ruling communist parties of Eastern Europe and the French and Italian parties (International: The Communist Information Bureau). Of limited payoff to Soviet policy, it was terminated in 1956.

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http://encarta.msn.com/encnet/refpages/RefArticle.aspx?refid=761572241&pn=2
http://linkinghub.elsevier.com/retrieve/pii/S0962629899000918
http://www.ingentaconnect.com/content/els/09626298/2000/00000019/00000005/art00091