Why did Marx think the state would eventually wither away?

In Marxism, Karl Marx argued that the primary function of the state is to serve as a tool for the ruling class to repress lower classes.1

Following a revolution, the proletariat would establish an interim "revolutionary dictatorship of the proletariat" to seize the means of production and prevent a counterrevolution by the displaced bourgeoisie. Marx believed that the state is inherently tied to class conflict; therefore, once the classless society is achieved and the threat of class-based opposition disappears, the state loses its purpose.231

Because the institution of the state exists solely to manage these class antagonisms, it is expected to "wither away" once those antagonisms are permanently resolved, ultimately giving way to a stateless and classless communist society.123