In proportion as the exploitation of one individual by another will also be put an end to, the exploitation of one nation by another will also be put an end to. In proportion as the antagonism between classes within the nation vanishes, the hostility of one nation to another will come to an end.

…

In place of the old bourgeois society, with its classes and class antagonisms, we shall have an association, in which the free development of each is the condition for the free development of all.

—Karl Marx & Friedrich Engels,
The Communist Manifesto
(1848)