A theory of international relations is a set of ideas that explains how the international system works. Liberalism and realism are two major theories of international relations. These two theories exhibit perceptions about war, foreign affairs and domestic relations. Realism focuses on state’s security and power, it emphasizes the role of the nation-state and makes broad assumption that all nation-states are motivated by national interests whereas liberalism is a political and moral philosophy based on the rights of the individual, liberty, consent of the governed and equality before law.

Realism is considered as a product of a long historical and philosophical tradition although its formulation as a theoretical approach to the study of international relations is a relatively recent. Thucydides an ancient Greek historian is closely associated with realism. He is said to have begun one of the main traditions of thinking about international relations. The history of the Peloponnesian war is a historical account of the Peloponnesian war written by Thucydides. Four of the essential assumptions of realism are found in this book, first the State is the principal actor in war and in politics in general, second the state is assumed to be a unitary actor he argues that once a state decides to go to war it speaks and acts with one voice. Third, decision makers acting in the name of the state are assumed to be rational actors. Fourth security is the primary consideration. There are many other scholars who have contributed to the development of realism. According to realism human individual is primarily fearful and power seeking. This type of characteristics are seen in an anarchic social environment where law abiding citizens are not fully protected against criminal and corrupt elements. According to realism states act as individuals might, meaning that each state acts in a unitary way in pursuit of its own national interests and the main national interest is power. These states exist in an anarchic international system the term anarchy means absence of an authoritative hierarchy since there is no higher political authority than the sovereign state which makes international system anarchic because of this realists argue that under this condition states in the international system can only rely on themselves. And in this type of international system the security of states is constantly under threat hence security becomes a primary objective of the state, the solutions to these problems are the balance of power which means when each state and each group of states having roughly equal power and Deterrence prevention of another state or a group of states from attacking a state or a group of states. Realist thinker Niccolo Machiavelli promoted the use of alliance and strategy to protect the state Thomas Hobbes contributed the idea that ‘states exist in an anarchic international system’. Morgenthau a realist thinker in mid-20^th century too saw international politics as a struggle for power. In 1970s Neorealism was developed by Kenneth waltz it gives importance to structure of the international system.

There are strengths and weaknesses of Realism it focuses on specifics parts of international reality (Anarchy, war and security and power) which makes it vulnerable to criticism from the supporter of international peace. It has four main weaknesses, first classical realist theory is based upon the idea that human nature is inherently bad and selfish, second its tendency to treat politics both within and between the states as involving unending competition for advantage third its lack of precisely explained theories of how governments of states make decisions the fourth weakness spans the state and international system levels, and consists of insufficient attention to the increased influence of non-state actors resulting changes at both of those levels over the past years. According to realism states pursue their own national interest or the best interest in its people but an excess in self-interest could lead to massive global instability because it will be an obstacle to maintain a peaceful international system.

Strengths of realism are it provides emphasis to practical knowledge it contributes to a powerful explanation on the nature of war, it recognizes every country as a sovereign entity it demonstrates how every country has a right to rule itself as a rational player in the realm of international relations.

Liberalism holds that human nature is basically good this goodness in humans make social progress possible including lasting peace, it considers war as a product of inadequate or corrupt social institutions and misunderstandings among leaders. Liberals believe that injustice, war, and aggression are not inevitable but can be moderated or even eliminated through institutional reform or collective action. League of Nations was an international institution which was founded by the liberals after the First World War to prevent war, United Nations is another such institution. Montesquieu and Immanuel Kant are two philosophers who have contributed to liberalism.in 19^th century liberalism supported democracy and free trade in 20^th century idealism contributed to liberalism. Woodrow Wilsons basic proposition was ‘war is preventable’, 20^th century can be credited with collective security. The aim of classical liberalism is to solve social problems, including international problems through good institutions.in times of peace liberalism gains greater validity because it had been unpopular during times of war and was revived by scholars like Robert Axelrod and Robert Keohane.

Liberalism focuses on an existing aspect of international reality however it focuses on a part of international reality one of strengths of liberalism is recognizes that war is costly and that is best to try for cooperation before resorting to war it contributes to maintaining peace and since it supports free trade, it helps to promote cooperation and peace. Collective security is a strength of the liberal theory it prevents the world falling into international anarchism and uphold human rights, democracy and a free market where people are free to trade however free trade has faced criticism since free trade between states of development can result in a relationship in which the less developed state is dependent on the more developed state and another weakness of liberalism is the imbalance of power and influence between states , the democratic peace theory points out that democracies do not go to war with each other one of the factors that has led to this point is that liberal states tend to be wealthier than non-liberal states which means they have less incentive to start war.

In conclusion, it is important to understand realism and liberalism have played a significant role in the international relations among countries, they both have their strengths and weaknesses, in an overall view realism describes international relations as a struggle for power among nations who seek to protect their own interests while liberalism offers an optimistic view of the global order it focuses on the peaceful part of international reality, its more about what the world ought to be.