The most important features of a society are its economic classes and their relations to each other in the modes of production of each historical epoch.
A class is defined by the relations of its members to the means of production.
Under capitalism, the capitalists own the means of production, the proletariat own only their capacity to work. Landlords rule the land, and the peasants are less significant than workers and are trapped in the idiocy of rural life. The proletariat definitely includes those who produce objects in factories with their hands, but Marxists dither about whether it includes people who work with their minds but are employees and live by their salaries.
History is the history of class struggles among the classes in society. New progressive classes arise that are related to new forms of production and struggle with the old. New forms of society arise appropriate to the new forms of production when the new classes win power. This doctrine is called historical materialism.
The state is the means whereby the ruling class forcibly maintains its rule over the other classes.
The successive stages of history include primitive communism characterized by equalitarian hunting and gathering, barbarism characterized by rule by chiefs, slave society with a slave class and agriculture, feudalism, capitalism, socialism and communism.
Most struggles in history are class struggles, even though the participants profess other goals. For example, protestantism reflects the rising capitalist class.
New classes usually win power by revolution. Revolutions are violent, because the dying ruling class doesn't give up power without a desperate struggle.
The capitalist class wins power over the feudal class by a bourgeois democratic revolution. A bourgeois democratic revolution is a good thing in its day, because it gets rid of feudal personal relations and replaces them by a cash nexus.
Capitalism creates the proletariat who have nothing to sell but their labor by bankrupting the artisan classes and the petty bourgeoisie and driving them into the proletariat.
The proletariat wins power by a proletarian revolution. According to Marx and Lenin, this revolution must be violent, because the bourgeoisie won't give up power by electoral means.
Neither Russia nor China had undergone a bourgeois-democratic revolution when the communists seized power. The communists undertook to build socialism anyway, and some of their rival socialists used the missing bourgeois-democratic revolution to predict that communist power would end badly.
Around the end of the 19th century Edouard Bernstein argued that it was possible to win power peacefully by winning elections. This was revisionism and the orthodox Marxist have used revisionism as an epithet ever since. "Revisionism" came to have more general meanings than Bernstein's actual doctrine, because it could be applied to people who denied Bernstein's doctrine but who could be accused of not being revolutionary enough.
Under capitalism the progressive class is the proletariat which is destined to overthrow capitalism and establish socialism, which will eventually evolve into communism.
Historical materialism is the Marxist methodology for interpreting history. The idea is to interpret all relations between groups of people as class relations and to interpret all conflicts as reflections of class struggles. A specific sequence of historical stages is part of the doctrine. It is (primitive communism, barbarism, slavery, feudalism, capitalism socialism, communism). Each stage of history has its own ruling class which uses the state to maintain its rule. Under feudalism the ruling class is the nobility, under capitalism it is the capitalists, and under socialism it is the proletariat. Primitive communism and communism are classless. In some countries oriental despotism happens as a stage distinct from feudalism.
The main feature of socialism is public ownership of the means of production, distribution and exchange.
Under capitalism, workers "tend" to be paid the bare amount required for them to support their families and reproduce. This is because of competition for jobs from the reserve army of labor, i.e. the unemployed.
The capitalist sells the product of the workers' labor at a price proportional to its value, which is the socially necessary labor required to produce it.
The difference between what the product sells for and what the workers are paid is surplus value and is appropriated by the capitalist.
Because the workers can't buy the full product of their labor and the capitalists don't consume all the surplus value, there tend to be recessions.
The steady increase in labor saving machinery creates unemployment and drives down wages. This emphasizes the tendency for there to be economic recessions. The tendency to pay the workers bare survival wages leads to the increasing immiseration of the proletariat.
The other classes, e.g. artisans and petty bourgeoisie, e.g. small shopkeepers, go broke and are driven into the proletariat. Even the smaller capitalists go broke.
Then a socialist revolution occurs. Originally this was supposed to occur first in the most advanced capitalist countries, e.g. Germany, Britain and the United States. It wasn't supposed to occur first in a backward country like Russia, where a bourgeois-democratic revolution should have happened first.
In the first stages of socialism the state is a dictatorship of the proletariat., i.e the proletariat rules the other classes by force.
The socialist slogan is "From each according to his ability, to each according to his work."
The communist slogan is "From each according to his ability, to each according to his needs."
Communism, which evolves peacefully from socialism, is a classless society under which the state will wither away.
Marx wrote
In a higher phase of communist society, after the enslaving subordination of the individual to the division of labour, and therewith also the antithesis between mental and physical labour, have vanished; after labour has become not only a means of life but life's prime want; after the productive forces have also increased with the all-round development of the individual, and all the springs of the co-operative wealth flow more abundantly - only then can the narrow horizon of bourgeois right be crossed in its entirety and society inscribe upon its banners: "From each according to his ability, to each according to his needs!" (K. Marx: Critique of the Gotha Programme)
Capitalism normally is replaced by socialism as a consequence of a proletarian revolution.
Prior to the overthrow of capitalism the proletariat must develop its own class consciousness. Other classes have their own forms of class consciousness.
Class hatred is a good thing and class collaboration is a bad thing.
Under capitalism, capitalist ideology penetrates other classes and must be struggled against by the proletariat.
Trade unions are good as training grounds for the class struggle, but it is capitalist ideology to suppose that they can make any permanent improvement in the condition of the proletariat. The belief that trade unions can make a permanent difference is a heresy called economism or trade-unionism, although the term may be due to Lenin.
The increasing exploitation of the working class leads to economic crises, because the working class cannot afford to buy the products of its labor. These crises get more intense with time. I forget whether the term general crisis of capitalism comes from Marx, but I rather think it comes much later. It refers also to imperialist wars
There is also a philosophy of history called historical materialism. Its main feature is the interpretation of history in terms of class struggle and historical progression in terms of revolutions in which a new ruling class takes over from the old ruling class.
It is all about Marxism---- changing the name to the "Fluffy Bunnies against Easter Eggs," as Walzer proposes will not change the ideology, rich vs. poor-- black vs, white--Latino vs the world--state vs corporations-- courts vs. legislators--it is an evil philosophy.