The chief reason warfare is still with us is neither a secret death-wish of the human species, nor an irrepressible instinct of aggression, nor, finally and more plausibly, the serious economic and social dangers inherent in disarmament, but the simple fact that no substitute for this final arbiter in international affairs has yet appeared on the political scene.

Hannah Arendt (1906-1975) German-American philosopher, political theorist

Essay (1969-02-27), “Reflections on Violence,” The New York Review of Books
    (Source)

Revised and collected in On Violence, ch. 1 (1970).