Class struggle is our starting point.
Since class divisions formed among humans thousands of years ago, class struggle has been the driving force of all major social change. While in any given society there may be a variety of different classes, the central struggle, the one that shapes all the others, is that between a class that produces the bulk of what the whole society needs, and a non-productive, parasitical class that controls production and steals the social product.
To defend their ruling position and assert their interests, a class must dominate the entire society: by claiming ownership and taking possession of the means of subsistence and production (land, waters, resources, factories, etc), holding political power to facilitate the running of their affairs and to repress dissent, and directing the flow of information and development of knowledge, persuading people through culture and education into understanding the arrangement as natural and desirable.
Owners and producers are the two fundamental classes of any class-divided society, because the struggle between them determines its mode of production, the parameters of how things are produced and distributed, as well as everything else that can go on in that society. Slave owners and slaves struggle for and against slavery. Landlords and serfs or peasants struggle for and against feudalism. Capitalists and workers struggle for and against capitalism.
Classes are defined and delineated by their struggles to continue existing from one day to the next. Capitalists struggle to take more of what the workers produce, in order to increase profitability and maintain competitiveness in relation to other capitalists. Workers struggle to keep more of what they produce, in the form of higher wages and benefits, so they can meet the needs of themselves and their families.
The fundamental classes are inherently antagonistic: the well-being of one comes at the expense of the other. There is no reconciling their interests. The struggle between them, as each class asserts its interests and is forced to adapt to the attacks of the other, drives the social changes that make up the narrative of human history.
The struggle of the dominating class is for preservation of their dominance. The struggle of the dominated class, whose survival is constantly and increasingly being undermined, is to improve their own conditions and ultimately for their emancipation. If they take control over the production they are already doing, and thereby overthrow the parasitical dominating class in a revolution, then new production relations can be established. The previous mode of production (slavery, feudalism, capitalism) comes to an end while a new one comes into being.
The productive forces that exist in each particular historical moment shape the way production can be carried out, which in turn defines the nature of each stage of that society. Productive forces include not only available resources, environmental conditions, and level of productive technology, but more importantly the knowledge and experience, political strength, and ideological consciousness of the laborers themselves.
This is why we must grasp that class struggle is not merely economic, and that its unfolding is not mechanically pre-determined, but must be a deliberate, comprehensive struggle against total social domination, involving the economic, political, and ideological fields. In other words, what is contested is not simply ownership and control and use of the means of production and the distribution of its output, but also political power, as well as the prevailing ideas with which we approach and interpret reality. These are intertwined and inseparable.
Thus far, when a dominated class has achieved emancipation from its specific relation to production, it has not been able to take over production overall. These revolutions have not eliminated the condition of class domination in general, but have instead led to the formation of new class divisions and dynamics. Some formerly dominated classes have remained dominated in altered relationships, and some have dominated others in turn.
Most emancipated slaves have continued to work land owned by others. When serfs, small farmers, and peasants are dispossessed of (“freed from”) their land, they are forced to sell their labor power, as workers, to capitalist enterprises. Even when peasants seize land from landlords, they tend to individualize land ownership and generate capitalistic practices of hiring labor for market-oriented production. When small producers and other members of the petite bourgeoisie (“middle classes” who possess some measure of social or material capital) seek to improve their lot, they succeed by becoming capitalists.
The central defining activity of capitalism is exploitation, when a worker is paid less than the value of what they produce, and the rest is privately appropriated (stolen) by capitalists, and reinvested as new capital. Workers fight exploitation constantly in their struggle for survival, but any gains are usually quickly wiped out because of the unorganized state of the working class and the presently greater strength of the highly organized capitalist class. Ending exploitation overall can only be accomplished by the self-emancipation from wage slavery of the working class as a whole.
The working class is the first class in history that has the potential to eliminate class divisions altogether. The key reason for this is that the means of production, while currently owned by a tiny minority, have been socialized; in other words they have been integrated into a global network and are wielded collectively by a global working class. If the working class as a whole gains control of it, and in the process constructs political power and ideological hegemony, they could collectively make decisions for the whole society, and produce not for private profit but for the common good. This would be the end of capitalism and the beginning of a new era.