Liberalism and realism have distinctly separate notions about the consideration of international phenomena. Liberalism regards the state as the primary basis of analysis, but also considers international law and organizations as well as nongovernmental groups as vital factors in addressing world politics. The most significant legacy of liberalism regarding international phenomenon is the pacification of foreign relations among liberal states (Snyder, 2010.) Liberalism considers international relations as a desirable system of interactions that present the possibility of mutual benefits. As a result, international behaviors that are both cooperative as well as peaceful are the ideal; the goal of such behaviors would be the establishment of alliances that are not inclined to fight each other. Nations are interdependent. By contrast, realism signifies the desire for coercive power that is usually seen in military terms, viewing states as the primary unit of analysis, while believing that the greatest potential threat to the individual state is the military power of other states. According to realism, although the rivalry between great powers may sometimes produce a stable international order, great powers will always continue to look to increase their share of power, so that if a favorable situation arises, they will undermine stability if necessary (Snyder, 2010.)
The rise and fall of the popularity of liberalism versus realism has occurred as a result of actual international events that support or contradict each train of thought. For example, the Vietnam War, with its tremendous number of casualties and divisiveness among the US population, led to a period of liberalism because people were tired of endless war, much as the situation today as a result of the Afghanistan and Iraq wars. Realism tended to surface during periods such as following World War II and the Cold War, when there was tremendous competition for dominance among nations, as well as fears about Germany and the Soviet Union and their attempts to dominate the world.