One of the two most dominant mainstream international relations theories. Realism has been around for a loooong time, but it's modern incarnation owes a lot to the 20th Century. In particular, modern Realism is the baby of the University of Chicago's resident misanthrope, John Mearsheimer. Mearsheimer is not just a "realist," but an "offensive realist." That's not to say he offends people; he's a proponent of the variety of realism called "offensive realism" (in contrast to "defensive realism.") There are multiple types of Realism, so it could be helpful to think of it as a "school" of thought rather than ONE concrete theory. For our purposes, offensive and defensive realism are worth knowing. 

Core ideas shared by both types of realism is that states are the most important actors, and that there is no other actor that can regulate or hold authority over states (sorry, UN.) Also that the so-called "international system" exists in a state of anarchy (there is no real regulating power on an international level.) Realists of all stripes also believe in a certain level of healthy mistrust; you can never truly know what another actor is thinking or what they're gonna do, so it is sensible to be cautious and not take things for granted. 

Defensive realism puts forward the idea that states work to survive by taking a defensive approach. The main theorist for defensive realism is Kenneth Waltz. Survival might mean building up the national defense, trying to stave off attack by building up a formidable supply of arms. Militaries are not for using but for making others think, "hey, do I really want to do this?" Defensive realists believe that any state that acts aggressively, however, will be "balanced" by others -- most states act to defend themselves and their interests and will seek to limit the rising power of a regional rival. In this sense, the international system "punishes" states that try to change the status quo. Finally, while defensive realists believe in a level of mistrust in global politics, they also think this mistrust rises and falls, and there are conditions where states may be able to let down their guard (with fellow members of a security alliance, for example.)

Offensive realism states that states attempt to guarantee their survival by pushing the boundaries of their power, to actively counteract others, rather than just working to survive. Think of it like a chess player who is really aggressive, rather than trying to protect their pieces. In this view, states are rewarded for being able to successfully expand their dominance. This leads to a world that is largely focused on the "great powers," states that have been able to expand their influence and exert their will. Military action is one way for states to show their dominance. The offensive realist view of mistrust in the international system is that states should always be looking over their shoulders -- no guarantee can be taken as a guarantee. 

A base idea shared by both types of realism is that states are the most important actors, and that there is no other actor that can regulate or hold authority over states (sorry, UN.)

The other of the two most dominant mainstream theories (and I think the more observable of the two) is Liberalism. Liberalism has also been around for a long time, getting its early, early start during the Enlightenment several hundred years ago. Whereas that early Liberalism focused on ideas of rights (eventually leading to the universal, inalienable idea of human rights in the 20th century), modern liberalism has been incorporated into international relations theory as the idea that states should seek cooperation and avoid conflict. It essentially boils down to the idea that global politics is not a zero-sum game (where there is a WINNER and a LOSER) and that states can mutually benefit. 

Wow, look how short this is compared to the Realist section. LOL. 

Liberalism is a bit easier to grasp, frankly -- cooperation > conflict, friends > enemies, surviving together > going it alone. 

A great example of a liberal worldview in action comes from the tail end of the Obama administration (he was in power from 2009-2017, but the key years here are around 2014-2016.) In that time, the Obama admin negotiated a nuclear energy agreement with Iran (alongside the EU and the International Atomic Energy Agency) and took steps to normalizing relations between the U.S. and Cuba. Just because those countries had been in ideological (and influence) conflict for 40+ years didn't mean there wasn't a way to work together and change relations. Then Trump came in and wrecked everything (but the Iran nuclear agreement kinda sorta endured, even after the U.S. left.) 

Cultural relativism is the belief that moral values, customs, and behaviors of a particular culture should be evaluated and understood within the context of that culture, rather than being judged by the standards of another culture. In other words, it is in opposition to universalism. In relation to human rights, cultural relativism argues that different cultures have different values and beliefs regarding human rights, and that there can be no universal standard that can be applied to all cultures, questioning the legitimacy of the universality of human rights. 

Supporters of cultural relativism argue that cultural diversity is important and that human rights should be understood and applied within the context of a particular culture. They often claim that the international human rights system is imposing Western values and beliefs on non-Western cultures, and that this practice can be harmful and disrespectful. For example, Western societies often place a lot of emphasis on individualism; many non-Western societies prioritize the community. Western ideas of Justice often have a defined sense of right and wrong, while some non-Western societies emphasize harmony in their attempts to find Justice. Most significantly, many non-Western cultures have different beliefs about gender roles and sexuality, making topics like women's rights and the promotion of equality for LGBTQ+ people quite controversial.

However, cultural relativism has been criticized by some who argue that it can be used to justify human rights violations in certain cultures. Critics argue that there are certain universal human rights that should apply to all people, regardless of their cultural background, and that cultural relativism can be used to deny these rights to individuals who are part of a particular culture.

Respecting cultural diversity while also protecting basic human rights is a continual challenge for the international system. 

Universalism is the belief that there are certain fundamental human rights that apply to all people, regardless of their cultural background or context. This perspective emphasizes the universality of human dignity and the idea that all individuals are entitled to certain basic rights, such as the right to life, freedom of speech, and freedom from discrimination.

In contrast to cultural relativism, universalism asserts that there are certain basic human rights that apply to all people, period. Different cultural backgrounds are not factored into the discussion. Universalists argue that cultural diversity should not be used as an excuse to deny or violate human rights, and that it is important to establish international standards and norms for the protection of human rights. The international system of human rights agreements is based on a universal standard of what rights people should have; that system was developed through the collaboration of many different countries and cultures. 

However, critics of universalism argue that it can be used to impose Western values on non-Western cultures, and that it can be culturally insensitive and disrespectful. They argue that cultural diversity should be respected, and that human rights should be understood and applied within the context of a particular culture. 

In summary, while cultural relativism emphasizes the importance of cultural context and diversity, universalism emphasizes the universality of human rights and the need for international standards to protect these rights. One of the greatest challenges to a universal approach to human rights is in the way that some countries claim that their cultures are incompatible with certain ideas (such as equality for women, fair treatment for people who are different, etc.) 

Capitalism is an economic system that is based on private ownership of the means of production, such as factories, land, and resources, and the creation of goods and services for profit in a competitive market. In a capitalist system, individuals and businesses have the freedom to own and use property and resources to create wealth, and prices are determined by supply and demand.

Capitalism has played a significant role in shaping global politics, as it has become the dominant economic system in much of the world. Many countries have adopted capitalist economic policies and embraced free market principles, leading to increased trade and globalization. Proponents of capitalism argue that it promotes innovation and growth, encourages individual initiative and entrepreneurship, and provides consumers with greater choice and better products.

However, critics of capitalism argue that it can also lead to inequality, exploitation, and environmental degradation. They argue that the pursuit of profit can often come at the expense of workers, consumers, and the environment, and that the benefits of capitalism are not equally distributed. They also point to the cyclical nature of capitalism, where periods of economic growth are often followed by periods of recession or stagnation. Critics of capitalism often highlight how in these recession periods, the wealthy and the holders of capital tend to be less-negatively-affected than the poor and the working class. 

Other critiques of capitalism highlight how the success of an economy is not necessarily an indicator of people's economic welfare. For instance, a company's stock price might soar after it fires thousands of people -- investors might look at that cut in jobs as a sign that the firm is saving money and cutting costs, and is therefore worthy of investment. The people who lost their jobs are more likely to be thinking about where their next paycheck will come from or when their health insurance will run out. 

Marxism is a political and economic theory developed by Karl Marx and Friedrich Engels in the mid-19th century. Marxism views history as a series of class struggles between the ruling class (the bourgeoisie) and the working class (the proletariat) over control of the means of production. According to Marx, capitalism is inherently exploitative and will inevitably lead to revolution and the establishment of a socialist society, where the means of production are owned and controlled by the workers.

In the context of global politics, Marxism has played a significant role in shaping leftist and socialist movements and political parties around the world. Many countries have adopted Marxist or socialist economic policies as a way to address issues of inequality, poverty, and exploitation, and to create more equal and just societies.

The Soviet Union, China, Cuba, and other countries adopted Marxist-Leninist or Maoist models of socialism, where the state controlled the means of production and distribution. However, these models have faced criticism for their lack of democracy and political repression. More recent economic and political policies inspired by Marxism have moved away from the 'central control' idea espoused by leaders in the USSR and China; "democratic socialism" is very much on the upswing in Western Europe and among some in the American left-wing (read: Alexandria Ocasio-Cortez.) In other words, full-throated Marxist systems have not been as successful as systems that blended Marxism with other, mainstream economic and political ideas. 

In recent years, there has been a resurgence of interest in Marxist ideas and principles, particularly in response to growing inequality and economic insecurity. Some argue that capitalism has failed to address these issues and that a Marxist approach is necessary to create a more just and equitable society.

Attention is paid to the importance of democracy, human rights, and individual freedoms, and a belief that socialism can be achieved through democratic processes rather than revolution. There is also a greater emphasis on decentralization and community participation in economic decision-making, with a focus on cooperatives, community-owned enterprises, and worker participation in decision-making.

One example of a modern implementation of Marxist ideas is the Nordic model of social democracy, which combines a market economy with a strong social welfare system and a commitment to equality and social justice. These countries have high levels of taxation and government spending on social programs, but also have relatively high levels of economic freedom and strong protections for individual rights and freedoms.

Overall, modern implementations of Marxist ideas seek to address the failures of previous models of socialism, such as lack of democracy, repression, and inefficiencies in economic planning, while still embracing the goal of creating a more equal and just society.