Sigmund Freud: Civilization; Die Weltanschauung, 1918

I may now add that civilization is a process in the service of Eros, whose purpose is to combine single human individuals, and after that families, the races, people and nations, into one great unity, the unity of mankind.
Why this has to happen, we do not know; the work of Eros is precisely this. These collections of men are to be libidinally bound to one another. Necessity alone, the advantages of work in common, will not hold them together. But man's natural aggressive instinct, the hostility of each against all and all against each, opposes this programme of civilization. This aggressive instinct is the derivative and the main representative of the death instinct which we have found alongside Eros and which shares world-dominion with it. And now, I think, the meaning of evolution of civilization is no longer obscure to us. It must present the struggle between Eros and Death, between the instinct of life and the instinct of destruction, as it works itself out in the human species. This struggle is what all life essentially consists of, and the evolution of civilization may therefore be simply described as the struggle for life of the human species.
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