marx 03Historical materialism
Historians in Marx's time thought that any human civilization could be explained by the products of the Spirit/the mind (arts, religion, politics, philosophy, humanities, etc. ) Marx asserted that men are work, and the only thing that explains civilization is the material  conditions of working men. Society consists of the base/infrastructure (the work) and an ideological superstructure (the intellectual stuff).
The base consists of two parts: productive forces and relations of production. Productive forces are workers/proletariat, technologies, sciences, tools. Relations reflect power structures: who owns the tools or technologies.  Marx stated that productive forces evolve faster than the relations.
An example of this would be the tension between the music industry and people who want to download and share digital music files. The relations of production evolve slowly because people with power fear losing it.
When the productive forces evolve in a way in which the relations become a burden, revolution occurs. This is what Marx called Historical Materialism, since it depends on the material conditions of the workers.