went along for the ride with democracy and trade, Russett and Oneal counted the number of IGOs that every pair of nations jointly belonged to, and they threw it into the regression analysis together with the democracy and trade scores and the realpolitik variables. The researchers concluded that Kant got it right three out of three times: democracy favors peace, trade favors peace, and membership in intergovernmental organizations favors peace. A pair of countries that are in the top tenth of the scale on all three variables are 83 percent less likely than an average pair of countries to have a militarized dispute in a given year, which means the likelihood is very close to zero.250
Might Kant have been right in an even grander sense? Russett and Oneal defended the Kantian triangle with sophisticated correlations. But a causal story derived from correlational data is always vulnerable to the possibility that some hidden entity is the real cause of both the effect one is trying to explain and the variables one is using to explain it. In the case of the Kantian triangle, each putative pacifying agent may depend on a deeper and even more Kantian cause: a willingness to resolve conflicts by means that are acceptable to all the affected parties, rather than by the stronger party imposing its will on the weaker one. Nations become stable democracies only when their political factions tire of murder as the means of assigning power. They engage in commerce only when they put a greater value on mutual prosperity than on unilateral glory. And they join intergovernmental organizations only when they are willing to cede a bit of sovereignty for a bit of mutual benefit. In other words, by signing on to the Kantian variables, nations and their leaders are increasingly acting in such a way that the principle behind their actions can be made universal. Could the Long Peace represent the ascendancy in the international arena of the Categorical Imperative? 251
FIGURE 5–25. Average number of IGO memberships shared by a pair of countries, 1885–2000
Source: Graph from Russett, 2008.
Many scholars in international relations would snort at the very idea. According to an influential theory tendentiously called “realism,” the absence of a world government consigns nations to a permanent state of Hobbesian anarchy. That means that leaders must act like psychopaths and consider only the national self-interest, unsoftened by sentimental (and suicidal) thoughts of morality.252
Realism is sometimes defended as a consequence of the existence of human nature, where the underlying theory of human nature is that people are selfinterested rational animals. But as we shall see in chapters 8 and 9, humans are also moral animals: not in the sense that their behavior is moral in the light of disinterested ethical analysis, but in the sense that it is guided by moral intuitions supported by emotions, norms, and taboos. Humans are also cognitive animals, who spin out beliefs and use them to guide their actions. None of these endowments pushes our species toward peace by default. But it is neither sentimental nor unscientific to imagine that particular historical moments can engage the moral and cognitive faculties of leaders and their coalitions in a combination that inclines them toward peaceful coexistence. Perhaps the Long Peace is one of them.
In addition to the three proximate Kantian causes, then, the Long Peace may depend on an ultimate Kantian cause. Norms among the influential constituencies in developed countries may have evolved to incorporate the conviction that war is inherently immoral because of its costs to human well-being, and that it can be justified only on the rare occasions when it is certain to prevent even greater costs to human well-being. If so, interstate war among developed countries would be going the way of customs such as slavery, serfdom, breaking on the wheel, disemboweling, bearbaiting, cat-burning, heretic-burning, witch-drowning, thief-hanging, public executions, the display of rotting corpses on gibbets, dueling, debtors’ prisons, flogging, keelhauling, and other practices that passed from unexceptionable to controversial to immoral to unthinkable to not-thought-about during the Humanitarian Revolution.
Can we identify exogenous causes of the new humanitarian aversion to war among developed countries? In chapter 4 I conjectured that the Humanitarian Revolution was accelerated by publishing, literacy, travel, science, and other cosmopolitan forces that broaden people’s intellectual and moral horizons. The second half of the 20th century has obvious parallels. It saw the dawn of television, computers, satellites, telecommunications, and jet travel, and an unprecedented expansion of science and higher education. The communications guru Marshall McLuhan