International Relations Theory
International Relations Theory

International Relations Theory

Lead Author(s): Serena Hicks

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In today's interconnected world, international politics affects everyone. Help students understand the complexities of international policy and politics.

Why International Relations?

One of the most divisive and discussed topics in politics is how to deal with other nations. Because these dealings intersect multiple areas of domestic policy and overlap issues of existential and human crisis, they are often considered issues of life and death. That isn't an exaggeration, since international relations is concerned with mainly two areas: economics and conflict. Both are deadly serious, and the two often collide.

Jewish Women  being led from Warsaw ghetto in the wake of  Warsaw Ghetto Uprising. Wikimedia/Public Domain​

At the core, international relations is the art and science of how nations deal with each other, but that often intersects in interesting ways with domestic political agendas, making what might have been a straight-forward issue into a thorny maze.

Understanding the theoretical underpinnings of international relations can help sort things out, as well as provide blueprints for dealing with difficult policy issues. Those blueprints are informed by political and moral beliefs, by cultural and social norms, and by the geopolitical realities each nation must face. 

For the beginning student of international politics, this course aims to give an overview of competing schools of though in international relations, and to describe some of the major issues. By the end of the course, the student should have a better understanding of the theoretical underpinnings of international relations, as well as an improved understanding of global politics and interactions, and a better ability to recognize trends in international relations.

World Map 2015 (The World Factbook)​

The Basics

To begin, we must first set out some definitions. First, we'll break down the components of international relations. Relations are any interactions, inclusive of economic, social, and conflictual activity. Inter meaning between (or among) and national. It turns out that defining a nation is a bit trickier and requires a little thought. Generally, a nation is defined as an aggregation of self-governing people confined by a defined border and sharing similar language, culture, or history. This seems obvious, but there are a lot of gray areas. For example, what constitutes sufficiently defined borders? The border between Argentina and Chile is still undefined along the Patagonian ice field between Cerro Murallon and Monte Fitz Roy. Since this border is not defined, does that exclude Argentina and Chile from national status? That seems unlikely, as both are recognized by other nations and in all other respects treated as nations. Also, there are several recognized nations which combine dissimilar tribal or ethnic groups (for example, Iraq, which includes Kurds and Arabs, both of are broken down further into tribal groups), but are still considered to be nations. On the other hand, a territory like Palestine - which is self-governing, and encompasses people with shared language, culture, and history - is not considered a nation (or, at least, isn't considered a nation by the United Nations). So while nations may be defined as stated above, the reality is that a nation is a nation when the international community treats it as a nation.  Which means that international relations is then somewhat murkily defined as any interaction between or among recognized nations, with the understanding that what constitutes any part of that is open for discussion. 

While that seems like a definition we can use, there are further complicating factors in determining what, exactly, is encompassed under the umbrella of international relations. As mentioned previously, there's a significant intersection between domestic and international relations, and it isn't always clear where the lines are drawn. As an example, consider the case of Syria. Syria is in the middle of a civil war, which is - at least theoretically - a domestic issue. It involves no other nations directly. However, it has significant impacts on other nations, particularly because of the actions of terrorist groups such as Daesh (for a discussion of this, see the supplementary material titled ISIS/ISIL/Daesh: A primer). At what point does a domestic issue become an international one? Does the international community have a right to interfere in the domestic workings of another state? Does it have an obligation to do so under certain circumstances? If there is such an obligation, what determines those rules? It's all very confusing.

In modern society, globalization argues for interconnectedness in ways which could conceivably make nearly all domestic politics an issue of international relations. Monetary policy and banking regulations in Germany affect credit and stock markets in Japan and the United States. Agricultural policy in Argentina affects Russia and China. Health care policy in the UK affects the countries of the EU and the British Commonwealth. Defense policy in India affects Pakistan, China, Afghanistan, and many others. Because of this web of intricate connections, it becomes difficult to untangle the boundaries. Thus, again, we find that what constitutes international relations is an evolving, case-by-case decision. The international community might interfere in Syria, but not Sudan.


The study of international relations, per se, cannot begin until nations exist (however ambiguous the idea of "nation" may be). When people began to form groups, first in family groups, then in tribes, there was no such thing as a nation. Even moving forward, nations didn't exist in the modern sense. Instead, there were empires and territories with borders which moved and flexed with each military campaign. Whatever a ruler could control at any given point was the limit of the territory. Without fixed borders, and encompassing conquered peoples paying tribute, these were not modern nations.

Assyrian Empire (From The Historical Atlas by William R. Shepherd, 1923, via Perry-Castaneda Map Collection)​

The competing empires in the ancient world gave way to the Greeks and then Romans in Europe. The breaking of the Roman Empire spawned a renewed round of territorial disputes in Europe. Feudalism took over as the dominant organizational structure, with feudal lords and loyalties changing depending on marriages, alliances, and various deals for land and power. Borders were fluid and governance malleable. During the same time period, religious changes created fault lines between Europe and the Middle East, with Europe falling primarily under the Roman Catholic Church, while the Christians in Asia Minor and the Balkans followed the Eastern Orthodoxy centered in Constantinople, in the Byzantine Empire. As Islam gained ground in Asia Minor and across Northern Africa, the power of the Byzantine Church waned, but the Roman Church grew, holding sway over rulers in Europe through a twist on the doctrine of divine right of monarchs, which stated that monarchs ruled by the grace of God, and since the Pope was God's representative on earth, the monarchs owed fealty to the Pope. This arrangement is what allowed the Pope to call Crusades (nominally to aid Byzantium in fending off Muslim invaders). The Crusades changed everything.

The Crusades sent insular European land holders into a strange new land. It introduced them to learning which had been lost to Europe for centuries, as well as to a wide variety of goods unknown in Europe at the time. Spices, silks, Egyptian cotton, and many other items caught the attention of the Crusaders. When they returned home, they'd developed an appetite for these goods. The city-states in what is now Italy were the first to take advantage of this new market, importing goods from the Middle East and selling them throughout Europe at a high price. It made the merchants wealthy while draining the coffers of feudal lords. 

The rulers of European feudal states began to consider their options. An age of exploration kicked off, fueled by a desire to find routes to the Orient and secure supplies of Oriental goods which didn't involve going through Venetian merchants. They began to establish colonies. At around the same time, in the Holy Roman Empire (more or less central Europe), a new Protestant movement was gaining momentum. The combination of economic and religious conflict proved a fertile ground for dispute, touching off numerous wars and conflicts. When the Holy Roman Empire tried to impose uniformity in religion, it sparked the Thirty Years' War in 1618. This conflagration swept up the entirety of Europe, adding to the ongoing longer war between Spain and the Netherlands, and drawing in England, France, Sweden, Russia, Denmark, the Ottoman Empire, and numerous principalities and feudal holdings.

In 1648, the major parties agreed to a series of treaties at Munster and Osnabruck which are collectively referred to as the Peace of Westphalia. The Peace of Westphalia changed the way Europeans perceived themselves and how they did business. It established the concept of settling treaties via diplomatic congress (that is, having diplomats meet and hammer out a peace accord to which the parties can agree), and it created a new conception of politics. The Peace of Westphalia introduced the idea of sovereign, independent nation-states, with set geographical boundaries and complete control over domestic affairs. This was the creation of what we now call the modern nation-state - or nation, in the case of international relations. 

The Ratification of the Treaty of Münster, 15 May 1648 (1648) by Gerard ter Borch​

As Europeans colonized the globe, they exported this conception of nation and borders to the rest of the world, carving up their territories along boundary lines which would eventually delineate new nations as colonies gained independence. In a very real sense, the entirety of international relations as conceived today is based on the conception of the state created at the negotiating tables in what is now Germany.

Peace of Westphalia

The Peace of Westphalia was important for the study of international relations because


it ended war in Europe.


it kicked off the race for colonies.


it established the Pope as the primary power in Europe.


it established the concept of nation-states.


Which of the following is NOT a characteristic of a nation?


well-defined borders


single ethnic group


cohesive self-government


shared history

What is Theory?

There are misapprehensions about what theory is. Theory is not a guess about how things work. It is an explanation of behaviors and actions supported by the information and evidence. Good theory has two primary goals: to explain and to predict. The first part of that - explanation - is all encompassing. A complete theory would explain all the behaviors and actions, while an incomplete theory only partially explains things. If we understand how things work, and can explain them well, we should be able to predict actions and behaviors. In physics, for example, the Theory of Relativity is well-supported by data and observation. More interestingly, it makes predictions about things we haven't yet seen or encountered. We can look for those things and find out if our theory predicted accurately. Accurate prediction is a sign that the theory is a good explanation of what's going on. 

In international relations, and in political science more generally, theory is not particularly well-developed. Because there are a lot of pieces of information (variables) involved, it's often difficult to explain and predict consistently and accurately. It's important to remember as we move forward to continually assess how good the theories are at doing the basic work of theory: how well do they explain and predict?

Question 3

What are the goals of good theory?


Present new information


Describe and explain behaviors and actions


Provide a framework for research


Explain and predict behaviors and actions

Some Important Background

There are a few points to clear up before we get into international relations. International relations is a discipline under political science, and as such, some terms are used differently than in more casual conversation. 


One of the most important concepts in international relations is power. The question of what power is (or is not) is fundamental to understanding international relations.

In order to understand what power is, you should first ask yourself what power does. The purpose of power is to control the actions of others - to make other actors do what you want them to do. In the context of international relations, this means other nations or states pursuing policies, platforms, or actions which are consistent with the needs and desires of your state.

If the purpose of power is to elicit behaviors consistent with the desires of the state, then it is important to discuss different types of power. There are many ways to "make" others do what you want - and the same is true of states.

Military power is the most obvious type of power. Military power is the use of military forces - both technological and manpower. There are differing types of military power. The US, for example, has substantially more advanced military technology and equipment as compared to most other nations. China, however, has more manpower than any other military. These different options within military power create different dynamics and different strengths for different military apparatus. These differences can (and do) often create substantial differences in the strategic focus of military organizations. A good example of this is the difference between the US and Soviet military approach to nuclear weapons. The US had (and has) superior technology, particularly in electronics. The Soviets had manpower, land mass, and resources associated with that land mass. Because of these differences in advantages, the US focused on creating extremely accurate, extremely reliable weapons, while the Soviets focused on creating extremely LARGE nuclear weapons. In strategic terms, the US focused on a counterforce strategy - using weapons to target specific targets to reduce the Soviet ability to bring force to bear. The Soviets, on the other hand, focused on a countervalue strategy - using weapons to target population centers and create massive casualties. Both are viable uses of military power - but the type of power employed is dependent not only on the resources available, but also the target state. Because the USSR had a much larger, dispersed population, trying a countervalue strategy against them wouldn't have been as effective as a counterforce strategy. Similarly, because US defenses and technology trumped Soviet technology, pursuing a counterforce strategy didn't make sense for the Soviets.

Economic power is the next most discussed type of power. Economic power is the ability to affect the domestic economic situation of another state, through trade, specific targeted sanctions, or similar mechanisms. As an example, China has a significant amount of economic power at this juncture because they are the source of the majority of manufacturing activity on the planet. The ability of the Chinese government to impact the domestic economic situation of other nations puts them in a position where they can influence the behavior of other governments. Economic power is most often exercised through trade agreements and aid (as incentives) and sanctions or tariffs (as hardships). Consider, for example, the international sanctions on North Korea which are aimed at curbing that nation's aggressive tendencies.

Technology is a newly emerging type of power. Not just technology in the sense of the tools used for military, economic, and diplomatic activity, but also technology as a source of power in and of itself. The rise of hacking and other types of technological attacks is evidence of this type of power.

Beyond these two primary types of power, there are a number of other influential types of power, including diplomacy, information, and moral suasion. Of these, diplomacy is the most commonly discussed, and can be thought of as the ability of a state to talk another state into doing what it wants. In the most basic terms, this is salesmanship. Information is a commodity, and sometimes nations want information others have. An example of using information as power would be espionage. The third influential power is moral suasion. This is using a morally superior position to try to convince others to do what is right. It is, effectively, taking the moral high ground. This, for example, is the primary type of power exercised by the Dalai Lama.

Aside from understanding what power is, the other key dimension of power is fungibility. Fungibility is using one thing as a proxy for, or to get, another thing. Some types of power are more fungible - flexible - than others. For example, economic power can be used to purchase a better military, better technology (or hackers), and to pay higher-quality diplomats. Military power can be used to acquire economic activity, and to intimidate or cow in a diplomatic setting. All types of power are fungible to a certain extent and in specific situations, but some types - particularly economic and military - are more fungible than others. That fungibility is one of the reasons these types of power are so desirable.


In political science, the term liberalism is distinctive from the term liberal when referring to political parties or ideology. There are actually three different ways we use liberalism in political science. Liberalism/liberalist theory is a theory of international relations which is the primary competitor of realism. In this context, liberalism refers to the underpinnings, predictions, and explanations associated with this theory. This is the usage which is most common in the first part of this text, which deals primarily with theories of international relations. 

A second use of liberalism is the use of the term in an economic sense. Liberal economics are the economics of the free market, as opposed to command economics or constrained economics. Liberalism in this sense refers particularly to the lack of constraint and regulation in markets - the more liberal the market, the fewer regulations. This is the usage of liberalism which will come into play when we discuss international political economy.

The third use of liberalism is the one most people use - the juxtaposition of liberal and conservative politics. In this usage, liberal refers to policies on the left side of the political spectrum. More accurately, liberal politics are those which seek change in politics, specifically in the areas of social issues and concerns regarding poverty, education, civil rights, justice, and civil liberties. This is a contrast to conservative politics which seek either to maintain the status quo on social issues or to return them to previous policies. Liberal politics are generally associated with more pacifist tendencies and conservative with more bellicose ones. These are terms which are not used often in international relations, since the concerns of liberal and conservative politics in this context are more usually domestic concerns rather than international one. However, there are some issues (which we'll discuss toward the end of the semester) where this distinction becomes important.

Republican and Democratic

In a similar situation, the use of republican and democratic (note the use of lower case letters here) do not refer to political parties or the platforms of those parties. Instead, republican and democratic here refer to the specific political terms. Republican refers to representative government, and democratic refers to voting behaviors and citizen-chosen government. In the united states, we have a democratic republic in the sense that individual citizens vote to choose representatives who then form the government. It is worth noting that a number of nations include these words in their names (Republic of Korea, the Democratic Republic of the Congo, etc.), but that doesn't necessarily indicate that the government follows that form.

Levels of Analysis

The final term we need to clarify before digging in is the concept of level of analysis. The level of analysis is the way social scientists, and particularly political scientists, talk about how the data and information is aggregated. What, exactly, are we looking at? In a more formal way, the level of analysis tells us the unit of measure for the thing we're studying.

There are three generally utilized levels of analysis. At the individual level of analysis  looks at individual people. This might be looking at specific leaders and their individual actions, or it might be looking at the actions of several people in individual way. Examples of individual level of analysis would include something like A Bright Shining Lie by Neil Sheehan which investigates the Vietnam war by looking minutely at John Paul Vann. The intersection of political science and history is very clear in individual biography, and those are the most commonly considered individual level analyses. The general presumption at this level of analysis is that the actions of individuals have major impacts on political outcomes, and that studying the psychology and situational factors, analysts can understand and predict actions.

The state level of analysis looks at forces acting within the state - domestic politics. Units of analysis here aren't individuals, but groups - ethnic, socio-economic, political, or other groups. Studies at this level often aggregate data and talk about the trends in groups. This is what is happening when national news agencies take polling data and discuss gender gaps or differences in support for a policy based on geography, gender, ethnicity, religion, or any other group characteristic. On the international relations front, these studies often focus on trends within states which might affect policy. An example of such a study might be one which looks at the trend toward fascism as a response to social and economic pressures in Europe prior to World War II. 

The third and final level is the system level of analysis. At this level, the unit of analysis is nations. This is where most of international relations discussions take place, thinking of states as unitary (acting as a single unit) and effectively discreet. Studies on the system level focus on interactions between and among nation-states, looking at data aggregated to represent each state. An example of this type of system level study might be a study investigating whether economic indicators such as Gross Domestic Product (GDP) and economic equality (GINI) predict whether a nation is more likely to go to war. 

We will revisit these levels of analysis throughout the semester, but it is important you understand the basics before we discuss theory - since the theories often dictate what level of analysis researchers use.