Truman Doctrine: Harry S Truman pledged a $400million fund to support any nation opposing Communism in 1947. It was first implemented in Greece and Turkey whose government were both engaged against communist guerrillas.
Marshall Plan: This was when secretary of state to Truman, George Marshall, set up a war relief fund to any nation trying to rebuild after WW2, although being open to all nations, including the USSR, Stalin refused aid as did General Tito of Communist Yugoslavia. The fund was supposed to be impartial (politically speaking) but from what I've read, the Americans gained alot of influence notably in West Germany and Japan.
NATO: NATO stands for the North Atlantic Treaty Organisation. It was set up in 1949 to oppose Communism on a military level and included all "western" countries eg: US, Canada, UK, W.Germany and most of western Europe. Its purpose was a common military and intelligence service against the Soviets. Its still very much in existence, although today it serves more to combat terrorism, and still excludes Russia.
All these plans and agencies were formed to "contain" communism, as in to stop the spread of communism from one country to another- this was called the Domino Theory. The Korean war in 1950 was seen as communism trying to spread from China (after the communist victory in the 1949 civil war) and so the US invaded (After the N.Koreans invaded S.Korea) "containing" the spread of communism. Containment conceded to the soviets that their methods of infiltrating and spreading communism was more effective that the US's attempts to spread democracy. The US was a reactionary force while the soviets were dictating where next they influenced.
NSC-68 was effectively a ratification of the policy of containment, expanding the US's military budget and developing the Hydrogen bomb as a policy of "deterrent".
The geopolitical limitations of the US's options in Asia and E.Europe was the fact that the soviets were simply much closer. It was easier for Stalin to control East Berlin than it was for Truman to control West Berlin, simply due to proximity. The USSR extended as far as east asia, and so it was easy for them to have a greater influence there too. They could easily send arms and personel to any region they pleased.
I hope I helped, the topic is very complex and would take me ages to write about coherently but ive a few pointers in there that should make writing the essay easier :)
