American believes that America is a virtuous and democratic state and role model, which should be followed by other states to become good states.
According to the realist view, it is a government foremost responsibility to use all means at its disposal ranging from democracy, threat of force and even war in order to seek the national interest. According to the realist national security and survival does not lie in idealism but rather in power of balance. The realist believe that in real politics it is essential need to pursue power at all cost by the states, however there must be a clear comprehension of what is achievable and what is not. The realists are concerned about security rather than think about cheating or lying. Their ambition is to tailor the US foreign policy according to the real world scenario rather than pursuing idealism. The realists believe that the Wilsonian idealism cannot promote peace and democracy in the arena of international politics.
During the early phase of Cold War the liberals saw optimism in three key areas: the role of institutions, the dominion of ideas and material prosperity. According to liberals the key institution, which can play a vital role in the international political affairs, can only be UN, which can decide the issues of inequality among the nations. If a weaker nation is invaded by a powerful nation, mediation can workout a solution. The UN could tackle the elementary causes of disparity and dissatisfaction and intercede between the parties. Thus for the liberals after WWII, there was no visible threat, democracy was spreading, so the basic concern of the nations should be the well being of the states and improving their economic condition.
As antagonism between the US and USSR existed long before WWII which was basically the ideological difference between two countries leading to Cold War. This hostility directed the course of events into to intense development and deployment and stock piling of nuclear weapons in both the countries. As both sides viewed themselves the champions of the world, they aggressively persuaded smaller nations to join their camp. In 1946 /1947 USSR brought communist regimes in Romania and Bulgaria. US felt threatened by the USSR violent approach and adopted the Trueman doctrine, which allowed US to help its allies and to contain the USSR expansion.
In 1959 the Vietnam War started and Vietnam became a hot bed of rivalry between the two great powers. The realist could no longer follow the liberal ideas as they saw the USSR expansion and its increasing power a serious threat to American security, and they decided to contain this expansion by all means. In early 1970s, after the advent of nuclear ICBMs it was no longer possible for both the super powers to conqueror each other. It was no longer possible to have the same view of the world as the Cold War has been pushed the world into a perilous age which US has never imagined.
This led to a military doctrine MAD (mutual assured destruction) and the idea behind this doctrine was that, the Western bloc will not be attacked as both superpowers have more than enough stockpile of nuclear weapons to wipe off each other from the face of earth, including all the human beings in the world. Thus the idea of attacking each other seemed a suicidal and unpractical act as a result nuclear weapon instead of threat worked as a Deterrence to