Forming the Eastern Bloc
During the opening stages of World War II, the Soviet Union laid the foundation for the Eastern Bloc by directly annexing several countries as Soviet Socialist Republics that were initially (and effectively) ceded to it by Nazi Germany in the Molotov–Ribbentrop Pact. These included eastern Poland, Latvia, Estonia, Lithuania, part of eastern Finland, and eastern Romania. In Asia, the Red Army had overrun Manchuria in the last month of the war, and went on to occupy the large swathe of Korean territory located north of the 38th parallel.
The Eastern European territories liberated from the Nazis and occupied by the Soviet armed forces were added to the Eastern Bloc by converting them into satellite states. The Soviet-style regimes that arose in the satellite states not only reproduced Soviet command economies, but also adopted the brutal methods employed by Joseph Stalin and Soviet secret police to suppress real and potential opposition.
Following the Allies' May 1945 victory, the Soviets effectively occupied Eastern Europe, while strong US and Western allied forces remained in Western Europe. In Allied-occupied Germany, the Soviet Union, United States, Britain and France established zones of occupation and a loose framework for four-power control . Soviet occupation of Eastern bloc states was viewed with suspicion by Western powers, as they saw this occupation as a sign of Soviet willingness to use aggression to spread the ideology of communism.
The Marshall Plan
In January 1947, the Truman administration created the Marshall Plan, which provided economic aid to rebuild war-torn Europe. Stalin opposed the Marshall Plan. He had built up the Eastern Bloc protective belt of Soviet controlled nations on his Western border, and wanted to maintain this buffer zone of states and a weakened Germany under Soviet control.
Fearing American political, cultural and economic penetration, Stalin eventually forbade Soviet Eastern bloc countries from accepting Marshall Plan aid. Stalin believed that economic integration with the West would allow Eastern Bloc countries to escape Soviet control, and that the US was trying to buy a pro-US re-alignment of Europe. The Soviet Union's alternative to the Marshall plan, which was purported to involve Soviet subsidies and trade with eastern Europe, became known as the Molotov Plan.
The Berlin Blockade
Stalin was also fearful of a reconstituted Germany; his vision of a post-war Germany did not include the ability to rearm or pose any kind of threat to the Soviet Union. In June of 1948, after the Marshall Plan and massive electoral losses for communist parties, Stalin instituted the Berlin Blockade (June 24, 1948 – May 12, 1949), one of the first major crises of the Cold War. In this blockade, the Soviets prevented food, materials and supplies from arriving in West Berlin. The United States, Britain, France, Canada, Australia, New Zealand and several other countries began the massive "Berlin airlift", supplying West Berlin with food and other provisions . In May 1949, Stalin backed down and lifted the blockade.