On Karl Marx's The German Ideology, Part I, an early, unpublished work from 1846.
What is human nature? What drives history? How can we improve our situation? Marx thought that fundamentally, you are what you do: you are your job, your means of subsistence. All the rest, this culture, this religion, this philosophy, is just a thin layer over our basic situation. Ideas are not primarily what changes the world; it's economics. In fact, you can't even have an idea that doesn't end up being in some way a product of your economic situation, and any given culture inevitably reflects and reinforces the interests of the rich within that culture. Marx saw history as following an inevitable progression driven by the division of labor and development of technology, which would inevitably lead to a situation so awful for the vast majority that we'll have no choice but revolution leading to Communist paradise.
OK, so that last part is a pretty big stretch, but some of Marx's diagnoses seem on point: our alienation from our jobs, the fact that our opinions really do more often than not reflect our situation and are not therefore the product of a wholly free intellectual choice, the fact that a lot of philosophy ignores our practical situation to its detriment (Marx really rips into the "Young Heglians" that were dominating German thought at the time), our general lack of self-knowledge (this idea among others being lifted from Hegel), and some of his analysis of past cultural advances (mostly lifted from Adam Smith). The original threesome of Mark, Seth, and Wes are back to hack into these issues and more. Read more about the topic and get the book.