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)
Marx believed that capitalism creates the proletariat class, who have nothing to sell but their labor. For a socialist state to happen, the proletariat must take power violently from those in command of the capitalist state. This is not a peaceful revolution. New classes win power through violent revolution. There is not a peaceful change in ideology. Most recent example would be the fall of the Soviet Union.
Those to claim that the democrats in office are now building a socialist state are wholeheartedly wrong. What they are witnessing is simple democracy and the whim of the people. It is the nature of democracy and a capitalistic society.
Communism evolves from socialism, according to Marx. Communist society is a classless society. Marx: Communism, which evolves peacefully from socialism, is a classless society under which the state will wither away. Socialist society is a classed society, albeit one without bourgeoisie society.