"War... is merely an idea, an institution, like dueling or slavery, that has been grafted onto human existence. It is not a trick of fate, a thunderbolt from hell, a natural calamity, or a desperate plot contrivance dreamed up by some sadistic puppeteer on high. And it seems to me that the institution is in pronounced decline, abandoned as attitudes toward it have changed, roughly following the pattern by which the ancient and formidable institution of slavery became discredited and then mostly obsolete."—from the Introduction

War is one of the great themes of human history and now, John Mueller believes, it is clearly declining. Developed nations have generally abandoned it as a way for conducting their relations with other countries, and most current warfare (though not all) is opportunistic predation waged by packs—often remarkably small ones—of criminals and bullies. Thus, argues Mueller, war has been substantially reduced to its remnants—or dregs—and thugs are the residual combatants.

Mueller is sensitive to the policy implications of this view. When developed states commit disciplined troops to peacekeeping, the result is usually a rapid cessation of murderous disorder. The Remnants of War thus reinvigorates our sense of the moral responsibility bound up in peacekeeping. In Mueller's view, capable domestic policing and military forces can also be effective in reestablishing civic order, and the building of competent governments is key to eliminating most of what remains of warfare.