How did the U.S. attempt to stop the spread of communism and influence international security during Cold War?

The Cold War, often dated from 1947 to 1991, was a sustained state of political and military tension between powers in the Western Bloc, dominated by the United States with NATO among its allies, and powers in the Eastern Bloc, dominated by the Soviet Union along with the Warsaw Pact. This began after the success of their temporary wartime alliance against Nazi Germany leaving the USSR and the US as two superpowers with profound economic and political differences. A neutral faction arose with the Non-Aligned Movement founded by Egypt, India, and Yugoslavia; this faction rejected association with either the US-led West or the Soviet-led East.

As the U.S. was the leading nation of the Western Bloc, they made strict restrictions to stop the spread of communism among the world, and those restrictions were compacted mainly by the Truman Doctrine and the Marshall Plan which I describe ahead.

TRUMAN DOCTRINE:

The intend of President Harry S. Truman by the Truman Doctrine was that the United States would provide political, military and economic assistance to all democratic nations under threat of comunism. As an effect the Doctrine gave a new direction to US foreign policy, from its usual scope of regional conflicts not directly involving the United States, to one of possible intervention in long distance conflicts. 

Truman said that the Cold War was a choice between freedom and oppression.   Therefore, Americans would have to abandon their decision not to get involved in European affairs; America was FORCED to get involved: 

Under the reality of a deteriorating relationship with the Soviet Union and the appearance of Soviet thoughts in Greek and Turkish affairs, the withdrawal of British assistance to Greece was the breaking point for the Truman Administration to reorient American foreign policy.

By this speech Truman reincorporated the Monroe Doctrine and led directly to the Marshall Plan.   It set a precedent for the principle of ‘collective security’ and NATO. 
It brought up the ‘Red Scare’ in the United States and in the USSR it convinced the Soviets that America was indeed threating Soviet Communism.

  

The Doctrine also embraced the policy of ‘containment’, meaning by this to keep trapped comunism within the boundaries of the USSR, and to avoid at any cost the spread within some other Nations. It was indeed a priority for the National Security of the US to stop the spread of comunist and totalitalian thoughts, since their security was depending in the clear break up with the traditional avoidance of commidtment with Western Hemisfere nations during periods of peace, the Truman Doctrine committed the US to support democratic nations to hold on political integrity obviously the US was receiving more hegemony and support back.

Marshall Plan:

After WW II, Europe was devastated. Millions of people died during this period of time, not just by war but because of poverty. There was no industry all along Europe, this meant no jobs or money to invest.   Transportation infrastructure were in ruins. This seemed to be the end of the old continet as a major poer. The only major power in the world that was not significantly damaged was the United States. 

Since 1945 and until 1947, the United States supported european economic recovery with direct financial aid.  Military assistance to Greece and Turkey was being given to prevent the spread of comunism in the region. 

Officially known as the European Recovery Program (ERP), the Marshall Plan was made to rebuild the economies of western Europe.  Marshall was convinced the key to restoration of political stability lay in the revitalization of national economies because in the long term he dimensioned political stability in Western Europe as a key to content the advances of communism in that region.  Besided they would become supporters of the ideology of the US in the Cold War.

The nations supported by the Marshall Plan were assisted greatly in their economic recovery.  From 1948 - 1952 European economies grew like never before in history.  Trade relations led to the formation of the North Atlantic alliance. Economic prosperity led by coal and steel industries helped to shape what we know now as the European Union.   

SOURCES:
http://history.state.gov/milestones/1945-1952/TrumanDoctrine
http://www.marshallfoundation.org/TheMarshallPlan.htm

American Studies Notes by Louis Monroy