A theory of international relations is a set of ideas that explain how the international system works. Unlike an ideology, a theory of international relations is (at least in principle) backed up with concrete evidence. The two major theories of international relations are realism and liberalism.


Realism, also referred to as Political Realism, is one of the oldest theories of international relations. It is considered the most dominant school of thought in IR.

Important Realists: Thucydides, Sun Tzu, Niccolo Machiavelli, Thomas Hobbes, E.H. Carr, Hans J. Morgenthau, et al.

In his “History of the Peloponnesian War,” Thucydides mentioned that the main reason for this war was the growth of Athenian power and the fear this caused in Sparta. (Security Dilemma)

Machiavelli, in his book ‘The Prince’ (1513), advised rulers to use deceit and violence as tools against other states.

Features: Realism claims the following:

1. The world is a harsh and dangerous place. The only certainty in the world is power. A powerful state will always be able to outdo – and outlast – weaker competitors. The most reliable power is military power.
2. A state’s primary interest is self-preservation. Therefore, the state must seek power and must always protect itself.
3. There is no power that can enforce global rules or punish bad behaviour.
4. Moral behaviour is very risky because it can undermine a state’s ability to protect itself.
5. The international system itself drives states to use military force and to war. Leaders may be moral, but they must not let moral concerns guide foreign policy.
6. International organizations and law have no power or force; they exist only as long as states accept them.

Realists are sceptical of morals and ethics and warn state leaders against sacrificing self interest for state’s external dealings, justifying political-leaders’ right to lie, cheat, kill, etc.

Classical Realism

  • It begins with Thucydides’ representation of power politics as a law of human behaviour.
  • Drive for power and the will to dominate are fundamental aspects of human nature.
  • These aspects are what drive the endless struggle for power in the international system and what causes the system to be anarchical.
  • Morgenthau is known for systemizing classical realism. One of his most famous works is “Politics Among Nations”.

Structural Realism

  • It asserts international politics is a struggle for power but does not endorse assumption that this is a result of human nature.
  • It attributes security competition and inter-state conflict to a lack of overarching authority above the states.
  • Power is a means to an end, main concern of states in national security, it posits.


  • It is composed of structural realism and relative and absolute gains.
  • It claims that states are interested in increasing power and influence (absolute gains) and will therefore cooperate with other states or actors to increase their capabilities.
  • States are also concerned with how much influence other states may achieve (relative gains).
  • Likelihood of states abandoning international agreements increases if states see others gaining more from the agreement.

Neo-Classical Realism

  • Contemporary challenge to structural realism.
  • Sceptical of the idea that international distribution of power can explain behaviour of states.
  • Since the end of the Cold War, realists have attempted to move beyond the assumptions of structural realists and incorporate additional facets located at individual and domestic level to explain international politics, such as the state-society relationship and perception of state leaders.

The Three S’s

  • State is the main actor and sovereignty is its distinguished trait.
  • Within the state sovereignty means that the state has supreme authority to make and enforce laws.
  • This is basic unwritten contracts between individuals and the state, e.g. trading liberty for security.


  • In international politics, the preeminent goal is survival.
  • Ambiguity as to whether accumulation of power is an end or a means, but universal agreement that ultimate goal of states is security.
  • Survival is a precondition to all other goals of a state.


  • International politics and domestic politics differ because in domestic politics, the citizens do not have to defend themselves.
  • In international politics, there is no higher actor than the state to prevent and counter the use of force.
  • Security, therefore, can only be realised through self-help.
  • However, in the course of providing for a state’s own security, the state in question will automatically fuel the insecurity of other states.


Liberalism emphasizes that the broad ties among states have both made it difficult to define national interest and also decreased the usefulness of military power.

It developed in the 1970s as some scholars began arguing that realism was outdated.

Liberal approaches to international relations are also called theories of complex interdependence.

Features: Liberalism claims the following:

1. The world is a harsh and dangerous place, but the consequences of using military power often outweigh the benefits. International cooperation is, therefore, in the interest of every state.
2. Military power is not the only form of power. Economic and social power, too, matter a great deal. Exercising economic power has proven more effective than exercising military power.
3. Different states often have different primary interests.
4. International rules and organizations can help foster cooperation, trust and prosperity.
5. The essence of liberalism is self-restraint, moderation, compromise and peace, often seen as the opposite of the essence of the international system.
6. It agrees with realists that war is a recurring feature of the anarchic state, as it has been for 300 years, following the Westphalian state system.
7. The centrality of other actors such as interest groups, transnational corporations and INGOs.
8. The image of IR is a cobweb of diverse actors.

Four-dimensional definition of Liberalism

It advocates for:

  • Rights of all citizens for equality, education, access to free press and religious toleration.
  • The legislative authority of the state possesses only the authority invested in it by the people.
  • The right of people to own property.
  • The most effective system of economic exchange is market-driven, not subordinate to bureaucratic control.


Commercial Liberalism: Advocates free trade and a market economy as the way towards peace and prosperity.

Republican Liberalism: Democratic states are more inclined to respect the rights of their citizens and are less likely to go to war with democratic neighbours. It is, currently, presented as democratic peace theory.

Sociological Liberalism: Notion of community and processes of interdependence are more important elements. As transnational activity increases, people and government from distant lands become more interdependent, make war more difficult and costly.

Neo-Liberal Institutionalism

Considered by many scholars to present the most convincing challenge to Realism and Neo-Realism, it suggests that the way toward peace and prosperity is to have independent states pool their resources and even surrender some of their sovereignty to create integrated communities to promote economic growth or respond to regional problems. It also shares many assumptions of Neo-Realism, however, believes that Neo-realism focuses too much on conflict and competition, minimising opportunities of cooperation.


Idealism is a specific school of liberalism that stresses the need for states to pursue moral goals and to act ethically in the international arena. Idealists believe that behaviour considered immoral on an interpersonal level is also immoral in foreign policy. Therefore, idealists argue that dishonesty, trickery and violence should be shunned. In the United States, idealism has usually been associated with the Democratic Party since World War I.


Marxism is based on the economic theory of Marxism, which arose from the thoughts of Karl Marx.


  • Aims to expose deeper truths.
  • Events in world politics (war, treaties, international operations, etc.) all occur within structures which have enormous influence on these events, the structures of the global capital system.
  • Argues that the effects of global capitalism are to ensure that the powerful and wealthy continue to prosper at the expense of the powerless and poor.
  • The view that the social world should be analysed as a totality – studying a single class or race is unhelpful without knowledge of all classes and races.
  • Materialistic conception of history – the processes of historical change are ultimately a reflection of the economic development of society.
  • Economic development is the motor of history.
  • Class also plays a key role in Marxist analysis, in contrast to liberals, who believe that there is harmony between various social groups.
  • Marxism holds that there is systematically bourgeoisie and the proletariat.

World Systems Theory

  • Capitalism has reached its highest and final stage, monopoly capitalism.
  • A two-tier structure had developed with a dominant core exploiting a less developed periphery.
  • The bourgeoisie of the core can use the profits from exploiting the periphery to improve the lot of the cores proletariat.
  • Wallerstein added the “semi-periphery” zone to the world systems theory.
  • This zone has an intermediary role in the world system, displaying features of both the core and the periphery.
  • The semi-periphery is dominated by core economic values, but has its own indigenously owned production base.


  • Theory produced by Italian Marxist Antonio Gramsci.
  • Produced no single integrated theoretical treatise; rather his intellectual legacy has been communicated through his prison notebooks.
  • Key question – Why had it been so difficult to promote revolution in Western Europe?

Critical Theory

  • Very similar to Granscianism but more concerned with issues relating to the sub-field of international political economy.
  • Involved with questions concerning international society, ethics and security.
  • Different from other Marxist theories because it is not concerned with further development of the analysis of the economic base of society.
  • Developed by the Jewish.
  • Concentrated on the questions relating to concepts of reason, rationality and the theory of knowledge.
  • Similar to constructivism with a communist twist.

Social Constructivism

  • Not a substantive theory of politics, but rather a social theory, more concerned with how to conceptualise the relationships between agents and structure – the relationships between states and the structure of international politics.
  • Doesn’t offer any theories on how states would/should act in certain circumstances, concerned with human consciousness and its role in international life.
  • Belief that actors are not born outside and prior to their social environment, instead produced and created by their social environment – nature not nurture.
  • Shapes what is viewed as a legitimate action thought the logic of consequences which attributes actions to the anticipated costs and benefits.
  • If an actor breaks the rules or acts in an illegitimate way, the costs of its actions will be higher – this is what encourages states to act correctly.
  • Most important part of Social Constructivism is norms.
  • The international structure is always changing and changes in three parts.

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