Which part of society's way of making things, not ideas or leaders, does historical materialism say is the main reason societies change their whole structure?

Historical materialism identifies the mode of production as the main reason societies change their whole structure. The mode of production refers to the specific way a society organizes its material life, meaning how it makes the things it needs to survive and thrive. This encompasses two key elements: the forces of production and the relations of production. The forces of production are the tools, technology, raw materials, and human labor that a society uses to produce goods. For example, in early societies, this might have been simple hand tools and human strength; in industrial societies, it's factories, machinery, and specialized labor. The relations of production, on the other hand, are the social relationships people enter into to carry out production. These are primarily economic and class relationships, defining who owns the means of production (like land or factories) and who has to sell their labor to survive. For instance, in feudalism, the relations of production involved lords owning land and serfs working it in exchange for protection. In capitalism, they involve capitalists owning factories and workers selling their labor for wages. Historical materialism argues that as the forces of production develop and become more advanced, they eventually come into conflict with the existing relations of production. This conflict creates tension and instability. For example, new technologies (forces of production) might allow for mass production, but the old social structures (relations of production) that limit who can own and benefit from these advancements can hinder progress. When this contradiction becomes severe enough, it leads to a social revolution, where the old relations of production are overthrown and replaced by new ones that are more compatible with the advanced forces of production, thus transforming the entire structure of society. It's the evolving, materialist process of how humans produce and organize that production, not abstract ideas or the personalities of leaders, that drives fundamental societal change.