The Cold War took shape as a battle between democracy/capitalism and communism over a period of six decades that by most accounts started before World War II between the two superpowers to emerge after the war, the United States and the Soviet Union.
However, communist insurgencies started to break out almost immediately in numerous areas. East Germany and the Peoples Republic of China, who both declared communist in 1949. East Berlin was also declared the capital of the new communist German Democratic Republic in 1949.
For more information on the United States presidents throughout the Cold War go to: http://www.npg.si.edu/exhibit/coldwar/coldwar.html
1940-1945– WWII in progress. OSS & cryptanalysts forerunners of US intelligence, Kim Philby Soviet double-agent, Igor Gouzenko embassy worker in Ottawa reports Soviet spy-ring
United States uses Atomic capability. Shows strength to Stalin.
For an excellent article about the “Plutonium box” used in the staging of the Nagasaki bombing go to:
Yalta Conference, the “Big Three” divide Germany.
1946– Communist insurgencies in China, Philippines, Clifford-Elsey Report
The Clifford-Elsey Report was an up-to-date analysis of US-Soviet relations in September of 1946 given to President Truman and helped to shape his approach to impending Cold War.
For the complete text of the Clifford-Elsey Report go to: http://www.trumanlibrary.org/whistlestop/study_collections/coldwar/documents/sectioned.php?documentid=4-1&pagenumber=1&groupid=1
1947– Truman Doctrine, Aid/alliance with Greece/Turkey begins, Red Scare begins, birth of CIA
1948– Czech, Malaya install communist regimes, Stalin blockades Berlin
1949– NATO formed, Red Scare peaks, Mao Zedong adds China to world communist rolls, East Berlin declared capital, Greeks first to defeat communism militarily.
For a great video from the period explaining the beginnings of the Cold War go to: