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.