By creating the world market, big industry has already brought all the peoples of the Earth, and especially the civilized peoples, into such close relation with one another that none is independent of what happens to the others. Further, it has co-ordinated the social development of the civilized countries to such an extent that, in all of them, bourgeoisie and proletariat have become the decisive classes, and the struggle between them the great struggle of the day. It follows that the communist revolution will not merely be a national phenomenon but must take place simultaneously in all civilized countries.
Friedrich Engels