It is said that the contradictions between capitalism and socialism are stronger than the contradictions among the capitalist countries. Theoretically, of course, that is true. It is not only true now, today; it was true before the Second World War. And it was more or less realized by the leaders of the capitalist countries. Yet the Second World War began not as a war with the U.S.S.R., but as a war between capitalist countries. Why? Firstly, because war with the U.S.S.R., as a socialist land, is more dangerous to capitalism than war between capitalist countries; for whereas war between capitalist countries puts in question only the supremacy of certain capitalist countries over others, war with the U.S.S.R. must certainly put in question the existence of capitalism itself. Secondly, because the capitalists, although they clamour, for "propaganda" purposes, about the aggressiveness of the Soviet Union, do not themselves believe that it is aggressive, because they are aware of the Soviet Union's peaceful policy and know that it will not itself attack capitalist countries.

[...] Consequently, the struggle of the capitalist countries for markets and their desire to crush their competitors proved in practice to be stronger than the contradictions between the capitalist camp and the socialist camp.

Joseph Stalin, Economic Problems of the USSR, Chapter 6 Inevitability of Wars Between Capitalist Countries