In the 19th century, Karl Marx and Friedrich Engels wrote that the main source of instability in the international system would be capitalist globalization, more specifically the conflict between two classes: the national bourgeoisie and the cosmopolitan proletariat. Historical materialism was going to be Marxism’s guideline in understanding the processes both in domestic and international affairs. Thus, for Marx human history has been a struggle to satisfy material needs and to resist class domination and exploitation. Despite ideological criticism, Marxism has strong empirical advantages on its side. Firstly, by emphasizing injustice and inequality it is very relevant to every period of time as these two failures of the human society have never been absent. Marxism is a structural theory just like neorealism, but it focuses on the economic sector instead of the military-political one. Its analysis reflects the relation between the base (the modes of production) and the superstructure (political institutions). The source of structural effects is not anarchy, but the capitalist mode of production which defines unjust political institutions and state relations.