The German philosopher Hegel, and Karl Marx, deepened the study of alienation (separation, estrangement, apart-ness), which began long before them. Plato, Aristotle, and many, many others have posed the question: Why are people pitted against one another?
 

Hegel addressed this question by setting up a metaphor: The Master and the Slave. It is not hard to develop a series of questions around this relationship like:

What does the Master want?

What does the Slave want?

What must the Master do?

What must the Slave do?

What does the Master want the Slave to know?

What does the Slave want the Master to know?

What does the Master want the Slave to believe?

What does the Slave want the Master to believe?
 

Hegel, earlier in life, had initiated his questions about alienation in regard to the estrangement of people from god. He asked, for example:

Why do people need priests, churches, and icons?

What is it that is really god?

How might people reach god without the barriers between god and them?
 

Marx sought to apply Hegel's questions to daily life, especially what he saw as the key factor of daily life, work, and the social relations that people establish when the engage with nature in the struggle to produce, and reproduce. Marx took up Hegel and suggested that the reason people are alienated from one another and from their work and creativity, in capitalist society, is because they do not own the means of production, the machines, factories, and workplaces where they must go in order to work to live. 
 

Marx said people are alienated when they do not control the process of production, when they do not control the products of their labor. Alienation, rooted in the individual ownership of what are really social means of production, causes people to be in a constant state of anxiety about employment, income, health, etc., denies them the chance to be fully free and creative in the most important sphere of their lives: work. Alienation pits people against one another at the outset in the struggle for jobs. Finally, the more that people engage in alienated work, which they must do to live, the more they enrich the people who do own the means of production, and impoverish themselves.
 

Because they are alienated, because what they see at the end of the day is the importance of commodities for sale, and not the importance of collective labor creating value, working people tend to focus on their relationships with things, as much or more than their relations with people.
 

At the same time, capitalists, who DO own the means of production, the banks, and land, are equally trapped. There is nothing they can do to offer, over time, free and creative jobs to the work force. Work sucks. Because the must compete, capitalists must use tactics like work speed-ups, battles for a longer work day, stripping the workers of control over the work place by replacing the workers' minds with the minds of the boss, and wage cuts. 
 

All this is the source of class struggle which was at the heart of Marx's analysis as well.