Pacifists ought to enter more deeply into the aesthetical and ethical point of view of their opponents. … So long as antimilitarists propose no substitute for war's disciplinary function, no moral equivalent of war, analogous, as one might say, to the mechanical equivalent of heat, so long they fail to realize the full inwardness of the situation. And as a rule they do fail. The duties, penalties, and sanctions pictured in the utopias they paint are all too weak and tame to touch the military-minded.

The Moral Equivalent of War (1906)