(Noma Bar for The Washington Post)

Ian Morris, a professor of classics at Stanford University, is the author of “War! What is it Good For? Conflict and the Progress of Civilization from Primates to Robots.”

Norman Angell, the Paris editor of Britain’s Daily Mail, was a man who expected to be listened to. Yet even he was astonished by the success of his book “The Great Illusion,” in which he announced that war had put itself out of business. “The day for progress by force has passed,” he explained. From now on, “it will be progress by ideas or not at all.”

He wrote these words in 1910. One politician after another lined up to praise the book. Four years later, the same men started World War I. By 1918, they had killed 15 million people; by 1945, the death toll from two world wars had passed 100 million and a nuclear arms race had begun. In 1983, U.S. war games suggested that an all-out battle with the Soviet Union would kill a billion people — at the time, one human in five — in the first few weeks. And today, a century after the beginning of the Great War, civil war is raging in Syria, tanks are massing on Ukraine’s borders and a fight against terrorism seems to have no end.

So yes, war is hell — but have you considered the alternatives? When looking upon the long run of history, it becomes clear that through 10,000 years of conflict, humanity has created larger, more organized societies that have greatly reduced the risk that their members will die violently. These better organized societies also have created the conditions for higher living standards and economic growth. War has not only made us safer, but richer, too.

Thinkers have long grappled with the relationships among peace, war and strength. Thomas Hobbes wrote his case for strong government, “Leviathan,” as the English Civil War raged around him in the 1640s. German sociologist Norbert Elias’s two-volume treatise, “The Civilizing Process,” published on the eve of World War II, argued that Europe had become a more peaceful place in the five centuries leading to his own day. The difference is that now we have the evidence to prove their case.

Take the long view. The world of the Stone Age, for instance, was a rough place; 10,000 years ago, if someone used force to settle an argument, he or she faced few constraints. Killing was normally on a small scale, in homicides, vendettas and raids, but because populations were tiny, the steady drip of low-level killing took an appalling toll. By many estimates, 10 to 20 percent of all Stone Age humans died at the hands of other people.

This puts the past 100 years in perspective. Since 1914, we have endured world wars, genocides and government-sponsored famines, not to mention civil strife, riots and murders. Altogether, we have killed a staggering 100 million to 200 million of our own kind. But over the century, about 10 billion lives were lived — which means that just 1 to 2 percent of the world’s population died violently. Those lucky enough to be born in the 20th century were on average 10 times less likely to come to a grisly end than those born in the Stone Age. And since 2000, the United Nations tells us, the risk of violent death has fallen even further, to 0.7 percent.

As this process unfolded, humanity prospered. Ten thousand years ago, when the planet’s population was 6 million or so, people lived about 30 years on average and supported themselves on the equivalent income of about $2 per day. Now, more than 7 billion people are on Earth, living more than twice as long (an average of 67 years), and with an average income of $25 per day.

This happened because about 10,000 years ago, the winners of wars began incorporating the losers into larger societies. The victors found that the only way to make these larger societies work was by developing stronger governments; and one of the first things these governments had to do, if they wanted to stay in power, was suppress violence among their subjects.

The men who ran these governments were no saints. They cracked down on killing not out of the goodness of their hearts but because well-behaved subjects were easier to govern and tax than angry, murderous ones. The unintended consequence, though, was that they kick-started the process through which rates of violent death plummeted between the Stone Age and the 20th century.

This process was brutal. Whether it was the Romans in Britain or the British in India, pacification could be just as bloody as the savagery it stamped out. Yet despite the Hitlers, Stalins and Maos, over 10,000 years, war made states, and states made peace.

War may well be the worst way imaginable to create larger, more peaceful societies, but the depressing fact is that it is pretty much the only way . If only the Roman Empire could have been created without killing millions of Gauls and Greeks, if the United States could have been built without killing millions of Native Americans, if these and countless conflicts could have been resolved by discussion instead of force. But this did not happen. People almost never give up their freedoms — including, at times, the right to kill and impoverish one another — unless forced to do so; and virtually the only force strong enough to bring this about has been defeat in war or fear that such a defeat is imminent.

The civilizing process also was uneven. Violence spiked up and down. For 1,000 years — beginning before Attila the Hun in the AD 400s and ending after Genghis Khan in the 1200s — mounted invaders from the steppes actually threw the process of pacification into reverse everywhere from China to Europe, with war breaking down larger, safer societies into smaller, more dangerous ones. Only in the 1600s did big, settled states find an answer to the nomads, in the shape of guns that delivered enough firepower to stop horsemen in their tracks. Combining these guns with new, oceangoing ships, Europeans exported unprecedented amounts of violence around the world. The consequences were terrible; and yet they created the largest societies yet seen, driving rates of violent death lower than ever before.

By the 18th century, vast European empires straddled the oceans, and Scottish philosopher Adam Smith saw that something new was happening. For millennia, conquest, plunder and taxes had made rulers rich, but now, Smith realized, markets were so big that a new path to the wealth of nations was opening. Taking it, however, was complicated. Markets would work best if governments got out of them, leaving people to truck and barter; but markets would only work at all if governments got into them, enforcing their rules and keeping trade free. The solution, Smith implied, was not a Leviathan but a kind of super-Leviathan that would police global trade.

After Napoleon’s defeat in 1815, this was precisely what the world got. Britain was the only industrialized economy on Earth, and it projected power as far away as India and China. Because its wealth came from exporting goods and services, it used its financial and naval muscle to deter rivals from threatening the international order. Wars did not end — the United States and China endured civil strife, European armies marched deep into Africa and India — but overall, for 99 years, the planet grew more peaceful and prosperous under Britain’s eye.

However, the Pax Britannica rested on a paradox. To sell its goods and services, Britain needed other countries to be rich enough to buy them. That meant that, like it or not, Britain had to encourage other nations to industrialize and accumulate wealth. The economic triumph of the 19th-century British world system, however, was simultaneously a strategic disaster. Thanks in significant part to British capital and expertise, the United States and Germany had turned into industrial giants by the 1870s, and doubts began growing about Britain’s ability to police the global order. The more successful the globocop was at doing its job, the more difficult that job became.

By the 1910s, some of the politicians who had so admired Angell’s “Great Illusion” had concluded that war was no longer the worst of their options. The violence they unleashed bankrupted Britain and threw the world into chaos. Not until 1989 did the wars and almost wars finally end, when the Soviet collapse left the United States as a much more powerful policeman than Britain had ever been.

Like its predecessor, the United States oversaw a huge expansion of trade, intimidated other countries into not making wars that would disturb the world order, and drove rates of violent death even lower. But again like Britain, America made its money by helping trading partners become richer, above all China, which, since 2000, has looked increasingly like a potential rival. The cycle that Britain experienced may be in store for the United States as well, unless Washington embraces its role as the only possible globocop in an increasingly unstable world — a world with far deadlier weapons than Britain could have imagined a century ago.

American attitudes toward government are therefore not just some Beltway debate; they matter to everyone on Earth. “Government,” Ronald Reagan assured Americans in his first inaugural address, “is not the solution to our problem; government is the problem.” Reagan’s great fear — that bloated government would stifle individual freedom — shows just how far the continuing debates over the merits of big and small government have taken us from the horrors that worried Hobbes. “The 10 most dangerous words in the English language,” Reagan said on another occasion, “are ‘Hi, I’m from the government, and I’m here to help.’ ” As Hobbes could have told him, in reality the 10 scariest words are, “There is no government and I’m here to kill you.”

To people in virtually any age before our own, the only argument that mattered was between extremely small government and no government at all. Extremely small government meant there was at least some law and order; no government meant that there was not.

I suspect even Reagan would have agreed. “One legislator accused me of having a 19th-century attitude on law and order,” Reagan said when he was governor of California. “That is a totally false charge. I have an 18th-century attitude. That is when the Founding Fathers made it clear that the safety of law-abiding citizens should be one of the government’s primary concerns.”

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