Someone (I don’t remember who) said that International Relations is the academic discipline of disagreement. Internationalists disagree on mostly everything, beginning by how to view their object of study. With that said, the discipline of International Relations has been historically dominated mostly by two theoretical schools, Realism and Liberalism. Some other minor schools, such as Constructivism and the English School also have significant influence. With that in mind, I believe it might be useful to post something here about the theory of International Relations.
Although the chronology is highly disputed, it can be defended that Realism is the first theory of International Relations, going back to Thucydides in Ancient Greece or to Machiavelli in late medieval/early modern Europe. In any case, Realism is arguably the most influential theory of International Relations, partially for its influence in actual statecraft (in opposition to academic thinking). Realists come in many shapes and colors, but I believe that most of them present some core characteristics:
The first thing that most (or in this case, all) Realists believe in is that the international system is anarchic. Actually, this is something that virtually any student of International Relations believes in, because… it is! When we say that the international system is anarchic, we are not saying that it is a mess or a state of permanent war. In international relations, the definition of anarchy is more simple: it means that there is no formal hierarchy of power between countries. Of course, countries have a clear hierarchy of power, with some being much more powerful than others. However, all countries are formally sovereign and independent. Countries recognize themselves as their ultimate authority. Each one of them.
A second thing that Realists believe is that countries (or in the more technical vocabulary, states) are the main actors of the international relations. Although we can speak of international corporations and international institutions, in the end, the actors that really matter are countries, especially great powers. That is so mainly because they have military capabilities. Coca-Cola may have lots of money, but not an army.
Finally, Realists believe that countries have a relationship of competition. They tend to see each other as potential enemies. Maybe not actual enemies, but certainly potential ones. Because of that, countries have to defend themselves against one another.
There are many more characteristics that we could add to this list, but I believe that these are the essential points of realist thinking in International Relations. Realists call themselves realists because they believe they see reality as it is, not in an idealized manner. I tend to agree. I believe that history proves that unfortunately, International Relations work in a realistic way. And this is something that, I believe, is key for at least many realists, and that is too often misunderstood: realists are not saying that international relations should be this way. They are saying that [sadly] they are this way. If you analyze international relations objectively, you will find out that countries (even the ones you like) and politicians (even the ones you believe are so nice) act in very selfish ways.
Realists are accused of leaving little or no room for change. But is this a fair assessment? I wish! But most other schools of International Relations fail to present plausible ways in which the international system could be improved, leading to more peace and prosperity for all.