Value-form
The Western Left academics are nowadays very happy to talk about "varieties of capitalism", but talking about "varieties of socialism" remains almost an absolute "no-no". Most Marxists continue to believe in "only one" (Marxian) socialism: either that, or nothing at all. "Either" a society or movement conforms to the true concept of socialism, "or" it does not; and if it does not, it "cannot be" socialism. However, precisely "because" there are many different Marxist beliefs about socialism, Marxists cannot agree among themselves whether Soviet-type societies were socialist, capitalist, or something else. Some countries meet with the moral expectations which Marxists have, and others do not.Originally Marx and Engels themselves had heckled the advocates of "true socialism", but later Friedrich Engels and Karl Kautsky promoted Marxist socialism as the one and true "scientific socialism" within the Socialist International. When he was 43 years old, Lenin stated: "The Marxist doctrine is omnipotent because it is true". Lenin's Communist International (a deliberate split with the social democrats) adopted Marxist socialism as its official political doctrine.
Communism
At the root of Marxism is the materialist conception of history, known as historical materialism for short. It holds that the key characteristic of economic systems through history has been the mode of production and that the change between modes of production has been triggered by class struggle. According to this analysis, the Industrial Revolution ushered the world into a new mode of production: capitalism. Before capitalism, certain working classes had ownership of instruments utilized in production, but because machinery was much more efficient this property became worthless and the mass majority of workers could only survive by selling their labor, working through making use of someone else's machinery and therefore making someone else profit. Thus with capitalism the world was divided between two major classes: the proletariat and the bourgeoisie. These classes are directly antagonistic: the bourgeoisie has private ownership of the means of production and earns a profit off surplus value, which is generated by the proletariat, which has no ownership of the means of production and therefore no option but to sell its labor to the bourgeoisie.