How did marx think that communism would come into fruition

Marx defined communism as the ideal target, the result after a very long process of transformation of the capitalist societies.

First of all, the proletariats, which are those who work for the owners of the means of production in exchange for a wage, should revolt against the exploitation they are suffering as employees. The businessmen are opressing the proletariats as they control their lives in two different manners, on their first hand they exercise direct control as their bosses and, secondly, because the social group they conform, known as the bourgeoisie, controlled the whole political and economical scenario.

They only solution was that the proletariats managed to uprise and gather all the power in society. This would allow to reach the intermediate step towards communism called 'Dictatorship of the proletariat', in which the proletariats have become owners of the means of production and are not dependent on working for the bourgeoisie anymore. Collective ownership is implemented instead.

Finally, the comunist society will be functioning when private property does no longer exists and everything is owned by all the citizens and therefore public, and when no government is needed, as having a goverment always would mean that a social class rules over the others. It will be an egalitarian society in which everybody has a job, receives a fair return for their work and there is no exploitation.