Marxism is both a critical approach that wants to always question the mainstream policy-driven approaches to IR theory and a classical approach via the philosophical and sociological tradition of its namesake, the philosopher Karl Marx (1818–1883). In fact, Marxism is the only theoretical perspective in IR that is named after a person. Of the range of great thinkers available to us, Marx may not automatically qualify as being the most ‘internationalist’. In fact, most of Marx’s (and his sometimes co-author Friedrich Engels’) work was not primarily concerned with the formation of states or even the interactions between them. What connected their interests to IR was the industrial revolution, as this event was ultimately what Marx was witnessing and trying to understand. He, with Engels, developed a revolutionary approach and outlined a set of concepts that transcended national differences while also providing practical advice on how to build a transnational movement of people. Workers from factories across the world – the proletariat – were to organise themselves into a politically revolutionary movement to counter the exploitative and unequal effects of capitalism, which were accelerated and expanded by the industrial revolution. This vision of a potential link between the bulk of humanity as a global proletariat is where, and how, Marxism enters IR from a different vantage point to other theories.