“Every war must end” was the title of defense analyst Fred C. Ikle’s 1971 book. Ikle became undersecretary of Defense for policy in the Reagan administration and his observation passed from insight to conventional wisdom. The Trump administration in its final weeks and the Biden government in its first months invoked the “all wars must end” axiom to justify withdrawing the last U.S. combat troops from Afghanistan. “We are not a people of perpetual war—it is the antithesis of everything for which we stand and for which our ancestors fought. All wars must end,” asserted Christopher Miller, acting secretary of...