Political theory is the study of concepts, assumptions, and principles used to define, explain, and assess political events, behaviors, and institutions.

Theories in international relations are frameworks of analysis, sets of concepts that
supplement understanding of what is going on, and why, between nations and states when they deal with each other.

• They attempt to explain interstate and international transactions.
• Theories also permit the examination of what is going on in world politics (international affairs), and allow us to compare one event to another.
• Part of a theory’s value (and, as a result, its popularity) lies in its ability to explain many cases, so that understanding is potentially clearer about the “what, where, how and why.”
• Sometimes theories are also used to analyze the impact of certain political or economic choices.
• Certain theories have become so well known and popular that they are accepted as paradigms.

Hobbes posited that without a powerful leader, man lives in a state of nature. The state of nature is the “war of every man against every man,” in which people constantly seek to destroy one another. There are no civil societies or states. This state of nature is so terrible and insecure that human beings then naturally seek peace.

Hans Morgenthau wrote on realist theoretical lines after World War II. Morgenthau, in Politics Among Nations: The Struggle for Power and Peace (1948), clearly set out six assumptions underpinning realism, based largely on political history. He argued that international relations are best viewed through the lens of the state quest for power.

Philosophically, Morgenthau’s realist thinking aligned with the views of two other men. These were Reinhold Niebuhr, a well-known American theologian and philosopher, and George F. Kennan, an American diplomat who promoted the policy of “containment” toward the Soviet Union and wrote the famed “X” or Long Telegram, formally The Sources of Soviet Conduct.

Idealism promotes toleration, reason and progress, equality before the law, and an open economy. It suggests that states would search for long-term mutual gains instead of short-term individual gains if their security and sovereignty were not significantly diminished or threatened. Idealism’s terms underlie liberal political thought.

Classical liberalism is a political philosophy and ideology in which primary emphasis is placed on securing the freedoms of the individual and limiting the power of the government.

One of the most prominent developments within liberal theory has been the phenomenon known as the democratic peace (Doyle). First imagined by Immanuel Kant, the democratic peace describes the absence of war between liberal States, defined as mature liberal democracies.

A newer, more modern approach that incorporates aspects of realism alongside other explanatory considerations is neorealist theory. Neorealism assumes that international relations and the patterns they tend to follow are shaped by the system’s structure, not so much by human characteristics. The ways power is distributed in the international structure shape world events. Internal or domestic activities and forces do not hold broad influence in the world the way that power does.

There are two basic principles underlying neorealism: first, the international system’s ordering principle is anarchy: there is no such thing as a world power superior to states. This results in an international system that is essentially a self-help system, with autonomous states that are functionally similar actors, each of which must always be prepared to defend or protect itself. The units (states) closely resemble each other in the functions they perform, the tasks faced, the primary goals they seek (with survival always being the fundamental goal and all other goals, including security, based on that survival), and how they go about accomplishing their objectives. Under anarchy, each state by and large operates on its own without having recourse to any higher authority to settle disputes and enforce law.

The second defining principle of the structure of international politics is the distribution of capabilities (power) across the units inhabiting the international system. Capabilities, or power, vary significantly between states; states, though functionally undifferentiated, are distinguished according to how much power they possess. Variations in power result in variations in the types and magnitude of structural constraints that states face, thereby leading to variations in how states behave or should behave.

Balance-of-power is a major concept in classical realism and in contemporary  eorealism. In general, balance-of-power theory holds that an extreme concentration of material power in the hands of single state or attempts by a state to conquer a region will provoke countervailing actions. These countervailing actions, called balancing, can take the form of alliance formation (external balancing) or efforts by individual states to increase their own relative power, generally through arms racing and military innovation (internal balancing). While balancing does not always operate efficiency to prevent the outbreak of war, it does help to maintain the stability of relations among states in the long-term.

The main points of neoliberalism include:

• The rule of the market  freedom for capital, goods and services, where the market is self-regulating allowing the trickle-down notion of wealth distribution. It also includes the elimination of unionized labor forces and removals of any impediments to capital mobility, such as regulations. The freedom is from the state, or government.
• Reducing public expenditure for social services, such as health and education, by the government
• Deregulation, to allow market forces to act as a self-regulating mechanism
• Privatization of public enterprise (from water to the Internet)
• Changing perceptions of public and community good to individualism and
  individual responsibility.

Marxism identifies the causes of war as class conflict, especially conflict between and within the capitalist class. Class, not the state or the individual, is the major unit of analysis in Marxist theory. Marxism presents a dialectical conception of human history: contradictions inherent in each historical epoch eventually lead to the rise of a new dominant class. The bourgeoisie or capitalist class dominates the era of capitalism, according to Marx. This era of capitalism will inevitably produce a proletarian, or working class, revolution. An era of socialism will follow, in which workers own the means of production. Eventually, there will be a classless, communist society in which the state, historically a tool of the bourgeoisie, will wither away. Many contemporary theorists have drawn on Marxist insights and categories of analysis, particularly in the study of on imperialism, dependency, and the world capitalist system.

Within the English School, there are two distinct accounts; these explain the actions and the aims of international society quite differently. The first is the pluralist account: it stresses the conduct of states within a condition of anarchy, yet it emphasizes that states, despite self-interest and egoism, do cooperate. It views a world with minimalist rules and focuses on protecting national sovereignty and on creating and maintaining world order. War is limited but not banned; instead, it is used to resist changes to the balance of power and to address violence against international society.
The second interpretation is the solidarist one: this can include a variety of theories assumptions and terms. Solidarists usually emphasize relationships between world society and international society; they tend toward the liberal approaches of International Relations. This is because the focus has been on the individuals inside the state as they impact the conduct of the society of states. Solidarists have included human rights, individual security, and peace as norms intensive foundations of international society. Some critical theorists have adopted the solidarist interpretation of international society so that the state still has theoretical presence and value, but they also wish to include human, global and related concerns in their analyses. They want to examine global communications and interaction. They tend to use the word “society” to separate their work from state-centered models.

International society has four goals which are preservation of international society, supporting the independence of member states, maintaining peace and helping secure the normative foundations of all social life. 

Critical theory does not seek to understand and explain like traditional theories do, but rather to analyze and change society. It seeks to remove domination, and to increase peace, freedom, justice, and equality. Its roots are to some extent in Marxism, with its approaches to the economy and society.

Emancipation is freedom from power, domination, and influence of others over a person or society. It includes efforts to obtain social, economic and/ or political rights or equality.

Constructivism has several iterations: it is a social theory, but it is also one with application to international relations. The idea was first suggested by Nicholas Onuf in 1989, and Wendt expanded on it in his 1999 book, Social Theory of International Politics. How states interact and how they apply restraint matters as does how they engage in “cultural internalization”. The degrees of cooperation and internalization by actors affect international relations.

He further indicates that constructivism in International Relations is not just about ideas and beliefs; state interests and power are formed via ideas and social interaction, too. Social interactions between states can lead to hostility and the security dilemma, or they may lead to more friendly relations, even under anarchy.

Three approaches to International Relations are:

• Empirical feminism, focusing on women or examining gender as a specific dimension of International Relations;
• Analytical feminism, taking up gender as a theoretical category to reveal and explore the gender biases of concepts, and to further explain the constitutive characteristics of International Relations; and
• Normative feminism, which reflects on the process of “theorizing as part of a normative agenda for socio-political change”.

Liberal feminists allege that difference feminist assertions are based on stereotypes of gender roles. Men and women are equal, according to them. Liberal feminists tend to examine the International Relations system less, and to explore women as subjects of study more: women in the military, women state leaders, and other women operating outside the traditional gender roles.