What were the chief ideas of Karl Marx?

Karl Marx was a German philosopher, economist, and revolutionary. He is perhaps most famous for writing and publishing The Communist Manifesto with Friedrich Engels. His theories and writing inspired the great communist revolutions of the nineteenth and twentieth centuries.

Marxism, a school of thought based on Marx's key teachings, holds that capitalist society is unsustainable and will eventually fall to a revolution. Marx believed that communism was the only model of society which had real longevity. Marx was very much influenced by the European revolutions and societies with great wealth inequality. As Marx described it, capitalist societies alienate laborers from their work and takes their sense of agency (control over the means and tools of production) out of their hands. Essentially, all wealth in a capitalist society is governed by a small, wealthy, elite class. Marx believed that such a society was unsustainable because it exploits and punishes laborers who have no real control over their productivity. Marx believed that the proletariat labor class of capitalist society would inevitably become so disgruntled with this system that they would overthrow the bourgeoisie ruling class and establish something more equitable.

Marx also described cultural production and reproduction as having three levels: economy at the base, ideology at the top, and culture in the middle, negotiating the relationship between the other two. Marx argued that religious ideology was "the opiate of the masses," meaning that people may be made complicit in their own oppression if they believe that it is natural and that some sort of reward for hard labor awaits them after death. This statement is directly influenced by the organization of pre-Revolutionary European societies. In Western Europe, the Catholic church taught that there was a natural, God-given order of society, including an entire class of people whose purpose was to labor in support of others. In this way, the economy was driven by the labor of the peasant class and reinforced by Christian theology. 

Today, Marxist studies has extended outside the realm of economics and into other forms of social sciences. Marx's writing suggests that we ought to consider the power structures in our lives that we take for granted and challenge those which are oppressive.