Historians consider the Treaty of Westphalia of 1648 not only to have put out the Wars of Religion but to have established the first version of the modern international order. Europe was now partitioned into sovereign states rather than being a crazy quilt of jurisdictions nominally overseen by the Pope and the Holy Roman Emperor. This Age of Sovereignty saw the ascendancy of states that were still linked to dynasties and religions but that really hung their prestige on their governments, territories, and commercial empires. It was this gradual consolidation of sovereign states (culminating a process that began well before 1648) that set off the two opposing trends that have emerged from every statistical study of war we have seen: wars were getting less frequent but more damaging.

A major reason wars declined in number was that the units that could fight each other declined in number. Recall from chapter 3 that the number of political units in Europe shrank from five hundred around the time of the Thirty Years' War to fewer than thirty in the 1950s. Now, you might think that this makes the decline in the frequency of wars just an accounting trick. With the stroke of an eraser, diplomats remove a line on a map that separates warring parties and magically take their conflict out of the "interstate war" books and hide it in the "civil war" books. But in fact the reduction is real. As Richardson showed, when we hold area constant, there are far fewer civil wars within national boundaries than there are interstate wars crossing them. (Just think of England, which hasn't had a true civil war in 350 years, but has fought many interstate wars since then.) It is another illustration of the logic of the Leviathan. As small baronies and duchies coalesced into larger kingdoms, the centralized authorities prevented them from warring with each other for the same reason that they prevented individual citizens from murdering each other (and that farmers prevent their livestock from killing each other): as far as an overlord is concerned, private quarrels within his domain are a dead loss. The reduction in the frequency of war is thus another manifestation of Elias's Civilizing Process.

In times of war…, the managers of full-fledged states often commissioned privateers, hired sometime bandits to raid their enemies, and encouraged their regular troops to take booty. In royal service, soldiers and sailors were often expected to provide for themselves by preying on the civilian population: commandeering, raping, looting, taking prizes. When demobilized, they commonly continued the same practices, but without the same royal protection; demobilized ships became pirate vessels, demobilized troops bandits.

The greater lethality of the wars that did take place was the result of a development called the military revolution. States got serious about war. This was partly a matter of improved weaponry, especially cannons and guns, but it was more a matter of recruiting greater numbers of people to kill and be killed. In medieval Europe and the Age of Dynasties, rulers were understandably nervous about arming large numbers of their peasants and training them in combat. (One can hear them asking themselves: What could possibly go wrong?) Instead they assembled ad hoc militias by hiring mercenaries or conscripting miscreants and ne'er-do-wells who could not buy their way out. In his essay "War Making and State Making as Organized Crime," Charles Tilly wrote:

The motto for the criminal, after all, is not a variation of "Semper fi," "All for one and one for all," "Duty, honor, country," "Banzai," or "Remember Pearl Harbor," but "Take the money and run." Indeed, for a criminal to perish in battle (or in the commission of a bank robbery) is essentially absurd; it is profoundly irrational to die for the thrill of violence and even more so for the procurement of booty, because you can't, after all, take either one with you.

As armed forces became more unified and permanent, they also became more effective. The thugs who had made up the earlier militias could hurt a lot of civilians, but they were not terribly effective in organized combat because bravery and discipline held no appeal. Mueller explains:

It also worked the other way: A king's best source of armed supporters was sometimes the world of outlaws. Robin Hood's conversion to royal archer may be a myth, but the myth records a practice. The distinctions between "legitimate" and "illegitimate" users of violence came clear only very slowly, in the process during which the states' armed forces became relatively unified and permanent.

But during the military revolution of the 16th and 17th centuries, states began to form professional standing armies. They conscripted large numbers of men from a cross section of society rather than just from the dregs at the bottom. They used a combination of drill, indoctrination, and brutal punishment to train them for organized combat. And they instilled in them a code of discipline, stoicism, and valor. The result was that when two of these armies clashed, they could rack up high body counts in a hurry.

The military historian Azar Gat has argued that "revolution" is a misnomer for what was really a gradual development. The process of making armies more effective was part of the centuries-long wave of technological and organizational change that made everything more effective. Perhaps an even greater advance in battlefield carnage than the original military revolution has been attributed to Napoleon, who replaced set battles in which both sides tried to conserve their soldiers with bold attacks in which a country would deploy every available resource to inflict all-out defeat on its enemy. Yet another "advance" was the tapping of the Industrial Revolution, beginning in the 19th century, to feed and equip ever larger quantities of soldiers and transport them to the battlefront more quickly. The renewable supply of cannon fodder stoked the games of attrition that pushed wars farther out along the tail of the power-law distribution.

During this long run-up in military power, there was a second force (together with the consolidation of states) that drove down the frequency of combat. Many historians have seen the 18th century as a time of respite in the long European history of war. In the preceding chapter I mentioned that imperial powers like Holland, Sweden, Denmark, Portugal, and Spain stopped competing in the great power game and redirected their energies from conquest to commerce. Brecke writes of a "relatively pacific 18th century" (at least from 1713 to 1789), which can be seen as a U in figure 5-17 and as a shallow lopsided W between the peaks for the religious and French wars in figure 5-18. Luard notes that in the Age of Sovereignty from 1648 to 1789, "objectives were often relatively limited; and many wars in any case ended in a draw, from which no country secured its maximum aims. Many wars were lengthy, but the method of fighting was often deliberately restrained and casualties were less heavy than in either the preceding age or subsequent ages." To be sure, the century saw some bloody combat, such as the world war known as the Seven Years' War, but as David Bell notes, "Historians need to be able to make distinctions between shades of horror, and if the eighteenth century did not exactly reduce the slavering dogs of war to 'performing poodles'…, its conflicts still ranked among the least horrific in European history."

As we saw in chapter 4, this tranquillity was a part of the Humanitarian Revolution connected with the Age of Reason, the Enlightenment, and the dawn of classical liberalism. The calming of religious fervor meant that wars were no longer inflamed with eschatological meaning, so leaders could cut deals rather than fight to the last man. Sovereign states were becoming commercial powers, which tend to favor positive-sum trade over zero-sum conquest. Popular writers were deconstructing honor, equating war with murder, ridiculing Europe's history of violence, and taking the viewpoints of soldiers and conquered peoples. Philosophers were redefining government from a means of implementing the whims of a monarch to a means for enhancing the life, liberty, and happiness of individual people, and tried to think up ways to limit the power of political leaders and incentivize them to avoid war. The ideas trickled upward and infiltrated the attitudes of at least some of the rulers of the day. While their "enlightened absolutism" was still absolutism, it was certainly better than unenlightened absolutism. And liberal democracy (which, as we shall see, appears to be a pacifying force) got its first toeholds in the United States and Great Britain.