This document provides an overview of the transition from WWII alliances to the tensions of the Cold War. It outlines the rise in tensions between the US/Britain and the Soviets over strategy during WWII. It then discusses key events that exacerbated tensions, including the spread of communism in Eastern Europe, the Truman Doctrine establishing the policy of containment against Soviet expansion, the Marshall Plan to rebuild Western Europe's economies, and the Berlin Blockade by the Soviets in 1948. Primary sources from Churchill and Stalin from 1946 are included to show the growing tensions between the former allies in their views of each other.