Another paradox, or as Macmillan puts it, an “uncomfortable truth,” is that it “brings both destruction and creation.” Advances in science and medicine have often been the result of wartime needs. Wartime demands likewise have accelerated social reforms. In particular, Macmillan points to the advancement of women in peacetime due to their wartime roles.

Macmillan is on shakier ground when she asserts that “during the Cold war, American political leaders, including Presidents Eisenhower and Johnson, accepted that they must do something for African Americans, not necessarily because they believed in the rightness of the cause,” rather because the Soviets “had a handy weapon for propaganda in American racial discrimination.” That certainly was not the motive in Johnson’s case, although as Robert Caro has clearly demonstrated, Johnson never fully shed his own racist impulses. Moreover, Macmillan overlooks Harry Truman’s critical role in desegregating the military, which was due more to his revulsion at the maltreatment of African Americans returning from World War II battlefields than to any concerns about Stalinist propaganda.

Macmillan offers multifarious examples of how “the need to make war has gone hand in hand with the development of the state.” Examples of war’s impact upon the nature of the state and its activities include the growth of bureaucracies to obtain and manage supplies and to organize and maintain support facilities. Similarly, the needs of war led to the emergence of the census, to identify numbers of potentially available troops. Macmillan attributes the notion, like the word itself, to ancient Rome, though the Book of Numbers likewise counts the males “between twenty and sixty years of age” who constituted the Hebrews’ fighting forces.

“There is some evidence,” writes Macmillan, that war also “brings social as well as economic leveling. Men and sometimes women are conscripted and thrown together with people unlike any they have ever met before.” Macmillan does not present that evidence, however. As is frequently her wont throughout the book, Macmillan instead cites several examples from World War I, in this case, to buttress her argument that mass conscription for war is a great societal leveler. Mass conscription no longer is the norm in several Western societies, however, including the United States, France, Britain, and the author’s native Canada—and it is unlikely ever to be reinstated. On the other hand, national service, even if not in the military itself, would generate the same social outcomes as conscription once did. With Western societies, especially the United States, becoming increasingly polarized, the case for conscription into national service has never been stronger.

“Greed for what others have, whether it is food for survival, women for servitude or procreation, precious minerals, trade or land, has always motivated war.” Nevertheless, even if war is hard-wired into the human psyche, and although human nature may not have changed since the mythical days of Hector and Achilles, and the very real ones of Napoleon and Wellington and of Foch and Baron von Richthofen, the context in which wars are fought is quite different. Similarly, the means with which they are fought are considerably more varied, depending on who is doing the fighting and how the fighting is being done. There are limits to the value of constantly referring to the battles and literature of ancient Greece and Rome, and, indeed to the period between 1870 and 1920.

MACMILLAN ASSERTS, “war has normally been seen as a sphere for men.” She does note that there have been women warriors throughout the ages, and not just the Amazons of Greek mythology. Still, until the recent past—and with few exceptions, such as the Israeli Defense Forces—women did not serve in military combat units. In the past, women certainly were an “excuse” for war, as she puts it (and sometimes for trying to sit it out, as Achilles sulked in his tent over Briseis). They still are in certain societies: witness the appalling and cruel behavior of ISIS fighters towards Iraq’s Yazidi women. Nevertheless, among major military powers, the absence of females in the military, due either to fear that they might be raped or due to their perceived lack of strength, is diminishing if not entirely gone.

Women fighters do continue to run the risk of rape, particularly if they are captured as prisoners of war. Despite that very real fear, however, women have graduated from combat support and service support roles to pilot fighter aircraft, serve on submarines and surface ships, operate in land force formations, and control drones. Most importantly, they have risen to very senior rank in Western militaries, including as American four-star generals and admirals serving as combatant and staff commanders.

Macmillan briefly recognizes this change but does not discuss it sufficiently. The availability of women for the military increases the talent pool of potential volunteers, while the expansion of high-technology jobs within the military reduces the requirement for all military entrants to be powerful physical specimens. As military operations continue to expand into the cybersphere and space, and as artificial intelligence and machine learning will occupy an increasingly important place in the command and control of military tactics and operations, the potential role of women on the battlefield will continue to expand. World War II’s Rosie may continue to be a riveter in a future conflict, supporting the military’s home front, but she will also be a targeter, a shooter, and an operational and field commander.

If the prospect of carrying off women like so many Sabines no longer is a major motivator for men to go to war, religion and ideology, or perhaps more accurately, religious ideology, still move men—and women—to risk their lives in war in order to save their and other people’s souls. Macmillan offers a quote from Martin Luther that could be the watchword of any Taliban or isis fighter: “The hand that wields the sword and kills with it is not man’s hand but God’s.” For far too long, postwar policymakers in the West, no doubt heavily influenced by the increasingly secularized societies in which they have lived, have paid little to no attention to the role of religion, especially when blended with nationalism, as a motivator for the use of force. Thus, senior American officials could authorize the supply of Stinger anti-aircraft missiles and other equipment to the Afghan Mujahedin without recognizing that in so doing they were arming an enemy that for subsequent decades would view itself at war with its erstwhile supporters.

Religion can be an excuse for crimes that might, in any event, be committed by their perpetrators. Yet there is no denying that it also does continue to spur to violence and war many who see themselves as true believers. Religion moved young Iranians to clear minefields with their bodies. It divided Catholics and Protestants in Northern Ireland for three hundred years until the signing of the 1998 American-negotiated Easter Sunday Agreement. Outbreaks of violence between Catholics and Protestants still take place wherever the Scottish Football League’s Celtic and Rangers play each other. Religion was a major factor in the most recent Balkan Wars between Orthodox Serbs and Catholic Croats and between Serbs and Muslims in Bosnia. It underlays the latest brutal civil strife in Yemen: the war between Zaidi Muslim Houthis located in the country’s north and the Sunnis of the south, reflecting tensions that go back a millennium. It fuels the ongoing, equally long, and certainly more brutal civil war in Syria, which pits Sunni rebels against the Alawi-dominated government. And, as already noted, it is a critical factor in the current and previous wars between Armenia and Azerbaijan, as well as in Turkey’s military assistance to the Azeris, thereby evoking the haunting specter of the early twentieth-century Armenian genocide.

Religion has led to the atrocities of Nigeria’s Boko Haram rebels, including the reported beheadings of Christians. It has propelled the emergence of isis and motivated young men from around the world to join its ranks. Macmillan mentions neither Yemen nor Nigeria; she tends to focus on the religious wars of Europe’s past. Yet what motivated past wars spurs current ones and no doubt future ones as well; the internet virtually guarantees that there will continue to be religious wars in the future.

Ethnic hatreds need not be religiously motivated or even have a religious component, however. That the Iraqi Kurds were Sunni like Saddam Hussein and his henchmen did not prevent the Iraqi dictator from launching airborne chemical strikes on Kurdish men, women, and children. Nor did it stop him from invading overwhelmingly Sunni Kuwait in 1990 or firing missiles at Wahhabi Sunni Saudi Arabia during that Gulf War. Neither was religion a factor in the 1994 Rwandan genocide that resulted in the death of as many as a million Tutsis. Rather, as in the Biblical story of Cain and Abel, the majority Hutus, most of whom were farmers, resented the elite minority Tutsis, who derived their wealth and status from their ownership of livestock. Macmillan’s European focus, ironically, like that of Pinker with whom she tends to disagree, overlooks that most horrific attempt to exterminate an entire people since World War II. The Rwandan genocide was the bloodiest massacre since the Cambodian killings perpetrated by Pol Pot’s Khmer Rouge, which were driven purely by ideology, and which Macmillan likewise fails to mention.