Famous spies like Alger Hiss, Harry Dexter White, Owen Lattimore, Harry Hopkins, and Philip Keeney funneled classified government documents to Soviet intelligence agencies. Some of these operatives were deliberate; others were unwitting dupes, who never quite understood what they were doing.
These “moles,” operating from their posts inside various governmental and social institutions, were ultimately complicit for thousand and tens of thousands of deaths as the USSR unfolded its imperialistic expansionism in eastern Europe, North Korea, and elsewhere.
Equipped with insider knowledge of the U.S. government’s policy-making apparatus, the Soviets could form their own policy in anticipation of American responses to it. As historians Stan Evans and Herbert Romerstein write,
Guided by such inside information, the Soviets could plan their own strategies with assurance — like a card player who could read the hand of an opponent. Knowing what the United States or other Western nations would do with respect to Germany, Poland, Spain, Japan, or China, the commissars could make their moves with foreknowledge of the responses they would get from other powers. Thus the two facets of the Soviet project interacted — the spying handmaiden to the policy interest. And, of course, if knowing what the policies of the United States and other non-Communist nations would be was useful to the Kremlin, then being able to influence or guide those policies in some manner would have been still more so.
Several concrete examples show this principle in action: At the Yalta Conference, Stalin knew that Roosevelt’s foreign policy was shaped largely by Alger Hiss, who was a Soviet agent. Stalin knew in advance Roosevelt’s concerns, and to which extent Roosevelt was willing to cede American interests to Stalin’s pressure tactics.
Similarly, Stalin knew that his operatives had undermined from within the will of the U.S. government to resist Mao’s vicious attack on Chinese liberty. Stalin could support Mao and know that the Americans would offer only slight verbal resistance and no material opposition. Millions of Chinese paid with their lives.