Explain the ideological and strategic origins of the Cold War and describe how the policy of containment shaped early U.S. action in Europe.
The wartime alliance between the United States and the Soviet Union did not survive victory for long. Stalin's Red Army occupied Eastern Europe as it pushed toward Berlin, and rather than allowing the free elections promised at Yalta, the Soviets installed loyal communist governments in Poland, Hungary, Czechoslovakia, and elsewhere. In a 1946 speech in Fulton, Missouri, Winston Churchill warned that "an iron curtain" had descended across the continent, dividing a free West from a Soviet-controlled East. That same year, American diplomat George Kennan sent a famous private analysis from Moscow -- the "Long Telegram" -- arguing the Soviet system was inherently expansionist and that the U.S. should respond not with war but with patient, firm "containment" of Soviet influence wherever it threatened to spread.
Containment quickly became official policy. The Truman Doctrine (1947) pledged American aid to any nation resisting communist takeover, starting with Greece and Turkey. The Marshall Plan (1947-1951) sent roughly $13 billion to rebuild Western European economies, on the theory that poverty and despair, not just tanks, were communism's best recruiting tools; the Soviet Union refused the aid and forced its satellite states to refuse it too. When the Soviets blockaded all land access to the Western-controlled sectors of Berlin in 1948 -- an island of freedom deep inside Soviet-occupied East Germany -- the U.S. and Britain responded not with force but with the Berlin Airlift, flying in food and coal around the clock for nearly a year until the Soviets relented. Germany formally split into a democratic West and a communist East in 1949, the same year the U.S. and its allies formed NATO, a mutual-defense pact, and the same year Mao Zedong's Communists won China's civil war -- a shock that convinced many Americans the Cold War was becoming a truly global struggle.
Mastery looks like: They can explain containment's logic, describe the Berlin Airlift's cause and resolution, and connect the 1949 Chinese Communist victory to rising American anxiety about global communism.
Common stumbles: Confusing the Berlin Airlift (1948-49) with the later Berlin Wall (built in 1961, a different unit entirely), or treating "the Cold War" as starting from one single dramatic event rather than a series of accumulating breaks in the wartime alliance.