Is it true to say that Marx and Engels had no systematic theory of international relations?.
To answer that question first of all, it would be useful to define the theory itself. According to the dictionary theory is a supposition to account for something, system of rules and principles; however theory can be also described as just a guess or assumption. In order to specify this broad definition, we should look at the theory in terms of international relations. Scholars have developed various sets of tools in order to make sense out of the international system. Ideally we would have a theory of the international system to which all scholars would give their broad assent, in the same way as all physicists accept the theory of relativity. Such levels of agreement are rare in the social sciences and unknown in the international relations. There is one suggestion why: as Chomsky has noted, in the analysis if international relation for example, the historical conditions are too varied and complex for anything that might plausibly be called "a theory- to apply uniformly. However, that only leads us to more questions with no definite answers: can the study of International relations be called a science or is the actual subject of it denies the existence of proof and one unarguable truth? In my view, IR theory has to have some level of structure, evidence and a strong, not neutral argument. Therefore, I would say that Marx and Engels had a theory. However, now I will try to examine how valid and systematic it was.
Probably no one would disagree with the fact that Marx and Engels have created a very strong theory that has affected the studies of sociology, politics, economics and many other spheres of life. It had a crucial role in the world history of the whole world, almost dictating the development of the twentieth century. Moreover, it is still continuing to influence peoples' minds.