Although all realists are concerned with foreign policy, not all realists include a foreign policy dimension in their theory. Thomas Hobbes, Han’s Morgenthau, Kenneth Waltz, and Stephan Walt are the among the most popular scholars in explaining the realist theory. Han’s Morgenthau is the 20th Century Realist and founder of classical realism. In his theory, his keystone is the concept of power and he stated that international politics is governed by the competitiveness and conflictual nature of humankind. Kenneth Waltz was the founder of neo-Realism and that he supports the proliferation of nuclear weapons in the sense that it could lead to international peace as they are individually secured and powerful if they acquire nuclear weapons. Realists explain foreign policy in terms of power politics due to human nature and international anarchy. They understand international politics as a struggle for power in international anarchy. This understanding of the international world has vital effects on how they understand foreign policy. Most importantly, they tend to understand foreign policy in terms of self-help policies aimed at maximizing national security. In this essay, I will discuss and analyze the realist views and the U.S. Foreign Policy. Realists hold that the proper purpose of the U.S. Foreign Policy is to secure America’s “national interest”. When it comes to U.S. Foreign Policy, they say that moral principles must be set aside and that those moral principles are incompatible. In the case of Khmer Rouge, that occurred in the mid-1970s, the secretary of State Henry Kissinger indicated that the U.S was prepared to continue its friendly relationship with the Khmer Rouge in a sense of balancing towards Vietnamese hegemony. In this case, although Cambodians were murderous thugs, they slaughtered more than 1.4 million Cambodians for not being communist, the U.S still try to maintain the relation and even tried to improve their foreign relations with Cambodia. In this case, according to realists, we can see that the U.S try to maintain its relations with Cambodia in order to secure its national interest. The US foreign policy decision during the Vietnam War directly contravenes the dictates of the realists’ theory. Because Vietnam was a minor power, and a weak state that, its loss to the communist bloc would have done almost nothing to improve the power position of the Soviet Union, or China for that matter, nor would it have harmed the power position of the United States. In this case, according to classical realism, the U.S. competitiveness such that the Soviet Union and China could improve the power position and harmed its position lead to intervene in the Vietnam war. On the other hand, according to domino theory in which to recognize minor powers as dominos, neo-realists argued that if all the dominoes joined the communist bloc, this would have increased its power by roughly one percent. In other words, Southeast Asia was not a strategically important region for the super power like the U.S. Therefore, the realist policy would have been to avoid military involvement there in this case. A classical realist, Hans Morgenthau described the U.S. policy at that time, as an indiscriminate crusade against communism. Thus, classical realism applied to the U.S foreign policy at that time that the power blocs struggling for power led U.S. to get tangled in Vietnam War. Similarly, in the Iraq war, following the 9/11 attack, classical realists argue that the U.S. should contain Iraq rather than going to war since Iraq is a minor power. But for U.S., it has interests in dominating Iraq oil which is the main interest for other major powers and the threat posed by the terrorists could affect its national security and this has led U.S. to attack Iraq. During Obama Administration, we can see the premises of the realist approach in efforts concerning Iran. Obama and his State Department are involved in a complex series of negotiations with the Iranian theocracy to cut a deal that will enable the regime to move forward with its nuclear program. This effort works towards balancing power between Israel and Iran. In this sense, neo-realist views apply to this case that having nuclear weapons could led to peace and stability in the international system than both sides are secured and no grudges could occur between the two sides. The neo-classical realist, Stephan Walt stated that the US should make its dominant position acceptable to others, by using military force sparingly, by fostering greater cooperation with main allies, and, most important of all, by rebuilding its descending international image. Moreover, he stated that the U.S should balance between the states as a referee and stop intervening in other states’ matters and intervene only if necessary and needed.To conclude, the foreign policy of every state is changing time to time depending on the leaders as well as the situation of the country at that moment and the same applies to the U.S. Most of the U.S foreign policies after the cold war tend to have liberal characteristics focusing on their national interest and welfare rather than focusing on their foreign policy and values as we can see in the case of Khmer Rouge and Iraq War. Anyhow, since Obama administration, the U.S. foreign policy tends to move towards realist ideas and now under Trump administration, it seems to be wondering between realist and liberalist approaches in my opinion.