I think that there were some significant elements behind China becoming Communist at the height of the Cold War.  The first was that the emergence of Sino- Soviet relationships on both diplomatic and ideological level became a reality for America to address.  This was intensified under Kissinger during the Nixon Administration, whereby American foreign policy became directly concerned with the triangulation of diplomacy between America, China, and the Soviet Union.  The more significant element of China becoming a Communist nation was that it wratcheted up the effort in the 1950s to ensure that Southeast Asia was protected from going Communist.  China helped to spawn the "domino theory" mode of thought in the State Department that if one nation of a particular region became Communist, the others would, as well.  Evidence of this could be seen in Truman's and Eisenhower's embrace of a type of "Pactomania," where diplomatic pacts were forged with governments of South-Eastern Asian governments to avoid them from becoming Communist.  This was significant because it moved the United States further from the ideal of moderation, one in which negotiation would become possible.  It also proved to be significant because the United States forged agreements with governments that were not legitimately supported by the people or authentic, rather being rooted in corruption.  The fear of more nations becomes Communist ended up feeding the desire of the United States to support non- Communist governments that were not aligned with American democratic ideals, making a feasible relationship with them difficult.  This was seen in the case of Vietnam and the doomed experience that was present within it.  In the end, the fear of other nations becoming Commuist as China did helped to drive foreign policy into a realm where judgment and long term vision were both sacrificed for short term hopes.