War has always stirred up passions. The intensity of combat, the charge of gunpowder, the specter of violent death — such things can’t help but elicit a suitably blazing mental response. “War is God,” says Judge Holden in Cormac McCarthy’s great frontier novel, “Blood Meridian.” “War is hell,” remarked Gen. William Tecumseh Sherman. Which, in the end, is it?

For the historian Margaret MacMillan, one of the world’s preeminent scholars of international relations, it’s not exactly either. Clearly averse to viewing history through such a moralizing lens, MacMillan prefers cold-eyed scrutiny. Her new book, “War: How Conflict Shaped Us,” portrays our capacity for conflict as neither divine nor demonic, but rather something intrinsic to humanity. “In understanding war,” she writes, “we understand something about being human.”

She offers up an enjoyable motley trot through many aspects of war: its origins in the struggle for resources or for power or simply for what philosopher Thomas Hobbes called “trifles,” its portrayal in popular culture (especially cinema), and the tactics and technology now transforming the way wars are fought. The book is light on political theory but rich in factual detail; entirely devoid of polemic, yet full of sober analysis. Humans are described as they are, not as they ought to be.

This is the approach of a traditional diplomatic historian, steeped in the realism predominant in her field. She prefers, characteristically, to avoid value judgments, though on occasion her own values slip out, as when she writes: “Great powers are not necessarily nice ones — why should they be? — but they do provide a minimum of security and stability for their own people.” This preference for realpolitik over idealism chimes with her previous work. “Peacemakers,” her award-winning account of the 1919 Paris Peace Conference, chided Woodrow Wilson for naively unleashing chaotic liberation movements around the world. And “Nixon and Mao” vindicated the hard-boiled Kissingerian machinations of the 1970s, when ideological belligerence gave way to a cold, calculated balance of powers.

Both of those books are narrative histories that dramatize how peace is hammered out. MacMillan, inevitably, now turns her mind to the nature of war. But this effort falls short of its predecessors. Originating as the prestigious Reith Lectures for the BBC (previous invitees: Robert Oppenheimer, John Kenneth Galbraith, Edward Said), it has no central narrative. That’s because a lecture series better lends itself to argumentation than storytelling. But since MacMillan is so suspicious of big ideas, “War” struggles to demonstrate a raison d’etre. For a scholar who seems happiest weaving a compelling story out of long-buried diplomatic papers, a book that contains no original, archival research has a diminished chance to shine.

If MacMillan allows herself one big idea, it is that “the capacity to make war and the evolution of human society are part of the same story.” The advent of computing and the Internet has military origins; the same is proving true of robotics and AI, which will define the future. Political evolution, for MacMillan, is equally indebted to war, which necessitated “the strong nation-states of today with their centralized governments and organized bureaucracies.” Taxation, parliaments, bond markets — all arose thanks to the untrammeled pursuit of war.

War and progress are inextricably linked for MacMillan, which puts her reluctantly at odds with a popular strain of progressive thought that holds that war is gradually being eradicated from the world. The Harvard polymath Steven Pinker’s 2011 bestseller, “The Better Angels of Our Nature,” cited throughout “War,” is the foremost recent expression of this view, containing the audacious claim that the 20th century, a period of two world wars and industrialized genocide, was in fact relatively peaceful.

MacMillan is too collegial to pick an outright fight with Pinker. Nevertheless, by showing how wars have advanced in lockstep with civilization, ever since they first really took off 10,000 years ago with the birth of farming and thus territorialism, MacMillan challenges his claim that there is a “civilizing process.” War is not the atavistic behavior we think it is; it is, alas, highly sophisticated — perhaps, MacMillan writes, “the most organized of all human activities.”

This skeptical, Hobbesian view of human nature, in which war is an “integral part of human experience,” may be unflattering to our species, but it at least keeps us on our toes. What Pinker and others call “the Long Peace” has lasted only since 1945, and, in a world of weapons of mass destruction, could be rendered redundant by a single, momentary ruthless act, just as World War I dashed the hopes of perpetual peace that had been encouraged by the century-long so-called Pax Britannica.

I say “so-called” because, as with the Cold War truce, it’s a dubious notion, which ignores ferocious imperialist wars fought outside Europe and America. MacMillan makes few references to colonialism in an otherwise reliable survey, and more non-Eurocentric sources would have broadened her book’s perspective. It’s worth noting, for example, that while hardly any Westerners today would agree with Judge Holden in “Blood Meridian,” the deification of violence — so medieval-seeming to us — persists in such modern guises as Maoism and jihadism, fueling ongoing conflicts from Peru to the Philippines.

And is this attitude really, in the end, so estranged from us? “War” won’t leave any reader feeling confident in postwar Western pacifist tendencies. We have glorified war since “The Iliad” at least, and our half-buried militarism could easily be disinterred for the right, or wrong, cause. Whenever we describe an achievement as “heroic” or a task as “herculean,” or discover an enemy’s “Achilles’ heel,” we betray a secret yearning for the gory battlegrounds of Troy as the touchstone of human conduct.


How Conflict Shaped Us

By Margaret MacMillan

Random House. 312 pp. $30