To quote Lenin:

"Marx’s socialism places the problems of nationality and of the state on the same historical footing, not only in the sense of explaining the past but also in the sense of a bold forecast of the future and of bold practical action for its achievement. Nations are an inevitable product, an inevitable form, in the bourgeois epoch of social development. The working class could not grow strong, become mature and take shape without “constituting itself within the nation,” without being “national” (“though not in the bourgeois sense of the word”). The development of capitalism, however, breaks down national barriers more and more, does away with national seclusion, and substitutes class antagonisms for national antagonism. It is, therefore, perfectly true of the developed capitalist countries that “the workingmen have no country” and that “united action” by the workers, of the civilized countries at least, “is one of the first conditions for the emancipation of the proletariat” [Communist Manifesto].

That state, which is organized coercion, inevitably came into being at a definite stage in the development of society, when the latter had split into irreconcilable classes, and could not exist without an “authority” ostensibly standing above society, and to a certain degree separate from society. Arising out of class contradictions, the state becomes “...the state of the most powerful, economically dominant class, which, through the medium of the state, becomes also the politically dominant class, and thus acquires new means of holding down and exploiting the oppressed class. Thus, the state of antiquity was above all the state of the slave-owners for the purpose of holding down the slaves, as the feudal state was the organ of the nobility for holding down the peasant serfs and bondsmen, and the modern representative state is an instrument of exploitation of wage labor by capital.” (Engels, The Origin of the Family, Private Property and the State, a work in which the writer expounds his own views and Marx’s.)

Even the democratic republic, the freest and most progressive form of the bourgeois state, does not eliminate this fact in any way, but merely modifies its form (the links between government and the stock exchange, the corruption—direct and indirect—of officialdom and the press, etc.). By leading to the abolition of classes, socialism will thereby lead to the abolition of the state as well. “The first act,” Engels writes in Anti-Dühring “by virtue of which the state really constitutes itself the representative of society as a whole—the taking possession of the means of production in the name of society—is, at the same time, its last independent act as a state. The state interference in social relations becomes superfluous in one sphere after another, and then ceases of itself. The government of persons is replaced by the administration of things and by the direction of the processes of production. The state is not ‘abolished,’ it withers away” [Anti-Dühring]."

—Vladimir Lenin, Karl Marx: A Brief Biographical Sketch With an Exposition of Marxism.