1. The Origins of the Cold War

2. Winston Churchill gave the Iron Curtain speech in 1946
Iron Curtain, the political, military, and ideological barrier erected by the Soviet Union after World War II to seal off itself and its dependent eastern and central European allies from open contact with the West and other noncommunist areas. 
Winston Churchill gave the Iron Curtain speech in 1946
Map of the Iron Curtain

3. The Truman Doctrine, 1947
The Truman Doctrine was an American foreign policy whose stated purpose was to counter Soviet geopolitical expansion during the Cold War. It was first announced to Congress by President Harry S. Truman on March 12, 1947 and further developed on July 12, 1948 when he pledged to contain threats to Greece and Turkey.
With the Truman Doctrine, President Harry S. Truman established that the United States would provide political, military and economic assistance to all democratic nations under threat from external or internal authoritarian forces. The Truman Doctrine effectively reoriented U.S. foreign policy, away from its usual stance of withdrawal from regional conflicts not directly involving the United States, to one of possible intervention in far away conflicts.
President Truman outlined the Truman Doctrine to a joint session of Congress in March of 1947

4. A map showing how the plan’s $20B was distributed by country
The Marshall Plan, 1947
In the immediate post-World War II period, Europe remained ravaged by war and thus susceptible to exploitation by an internal and external Communist threat.
Fanned by the fear of Communist expansion and the rapid deterioration of European economies in the winter of 1946–1947, Congress passed the Economic Cooperation Act in March 1948 and approved funding that would eventually rise to over $12 billion for the rebuilding of Western Europe.
Photo shows a delivery of wheat from the U.S. being unloaded in Rotterdam, Netherlands
A map showing how the plan’s $20B was distributed by country

5. NATO Treaty, 1949. Warsaw Pact, 1955.
The North Atlantic Treaty Organization was created in 1949 by the United States, Canada, and several Western European nations to provide collective security against the Soviet Union.
The United States viewed an economically strong, rearmed, and integrated Europe as vital to the prevention of communist expansion across the continent. 
The Warsaw Treaty Organization (also known as the Warsaw Pact) was a political and military alliance established on May 14, 1955 between the Soviet Union and several Eastern European countries. The Soviet Union formed this alliance as a counterbalance to the North Atlantic Treaty Organization (NATO)
The original signatories to the Warsaw Treaty Organization were the Soviet Union, Albania, Poland, Czechoslovakia, Hungary, Bulgaria, Romania, and the German Democratic Republic. Although the members of the Warsaw Pact pledged to defend each other if one or more of them came under attack, emphasized non-interference in the internal affairs of its members, and supposedly organized itself around collective decision-making, the Soviet Union ultimately controlled most of the Pact’s decisions. 

6. Central Historical Question
Who started the Cold War?