What is the materialist conception of history?

Your question may refer to two things: a way of studying history through material goods or a social theory described by Karl Marx.

First, a materialist perspective of history would place emphasis on the material goods created throughout space and across time. Historians, archaeologists, anthropologists and the like may use material goods as a means of determining the values, beliefs, and means of production in a society.

As an example, let's consider pottery in the Roman Empire. Prior to integration into the Roman Empire, much of Europe had distinctive, local styles of pottery. After integration, both material and social culture were effectively "Romanized." Pottery found in the British Isles and the heart of Rome would look quite similar, because using Roman style pottery was a way that people participated in their Roman identity. After the fall of the Empire in the West, localized styles once again came into fashion. This period of (more) uniform material culture tells us that people in the Roman Empire felt that the everyday objects in their lives were fundamental to the way they manifested their Roman identities. Additionally, it can let us know that there were trade networks which allowed for the spread of Roman styles and material goods.

The other concept your question might refer to is a social theory outlined by Karl Marx. This concept is called "historical materialism" argues that all cultural change or growth is driven by economic and material means. Marx believed that all economic systems (aside from Communism) would eventually be at odds with the ideologies it produced, and the system would collapse and be replaced. Marx's historical materialism draws on the idea I described above, where material goods are a means of expressing beliefs and values. Additionally, Marx felt that the production of material goods is a means of reproducing elements of culture. In other words, the goods we create throughout out lives (directly or indirectly) both are determined by our culture and help to reinforce that culture.

Marx's theory of historical materialism is directly related to many of the European revolutions of the eighteenth and nineteenth centuries. Let's use the French Revolution as an example: the labor of the peasant class was exploited for the benefit of the nobility, and this system was reinforced by an ideology which framed this as the God-given order of the world. In reality, this ideology developed as a result of the socioeconomic system, not the other way around. The laboring peasant class revolted against the nobility in favor of a more egalitarian state, replacing the old system of economic (re)production with a new one.