seized and transferred most of Germany's industrial plants and it exacted war reparations from East Germany, Hungary, Romania, and Bulgaria, using Soviet-dominated joint enterprises. It used trading arrangements deliberately designed to favor the Soviet Union. Moscow controlled the Communist parties that ruled the satellite states, and they followed orders from the Kremlin. Historian Mark Kramer concludes: The net outflow of resources from eastern Europe to the Soviet Union was approximately $15 billion to $20 billion in the first decade after World War II, an amount roughly equal to the total aid provided by the United States to western Europe under the Marshall Plan. Moscow considered Eastern Europe to be a buffer zone for the forward defense of its western borders and ensured its control of the region by transforming the East European countries into subservient allies. In 1956, Soviet troops crushed a popular uprising and rebellion in Hungary and acted again in 1968 to end the Czechoslovak government's Prague Spring attempts at reform. In addition to military occupation and intervention, the Soviet Union controlled Eastern European states through its ability to supply or withhold vital natural resources. Espionage All sides in the Cold War engaged in espionage. The Soviet KGB ("Committee for State Security"), the bureau responsible for foreign espionage and internal surveillance, was famous for its effectiveness. A massive network of informants throughout the Soviet Union was used to monitor dissent from official Soviet politics and morals. Historian Raymond L. Garthoff concludes there probably was parity in the quantity and quality of secret information obtained by each side. The Soviets probably had an advantage in terms of HUMINT (espionage) and "sometimes in its reach into high policy circles." Did it matter? In terms of decisive impact Garthoff concludes: We also can now have high confidence in the judgment that there were no successful “moles” at the political decision-making level on either side. Similarly, there is no evidence, on either side, of any major political or military decision that was prematurely discovered through espionage and thwarted by the other side. There also is no evidence of any major political or military decision that was crucially influenced (much less generated) by an agent of the other side. in terms of the impact of intelligence on national policy it was not so much the minute details, or capture of top-secret plans that mattered most. Instead, every major country used its intelligence services