Enlightenment Now: The Case for Reason, Science, Humanism, and Progress

The peaks in the graph correspond to mass killings in the Indonesian anti-Communist “year of living dangerously” (1965–66, 700,000 deaths), the Chinese Cultural Revolution (1966–75, 600,000), Tutsis against Hutus in Burundi (1965–73, 140,000), the Bangladesh War of Independence (1971, 1.7 million), north-against-south violence in Sudan (1956–72, 500,000), Idi Amin’s regime in Uganda (1972–79, 150,000), Pol Pot’s regime in Cambodia (1975–79, 2.5 million), killings of political enemies in Vietnam (1965–75, 500,000), and more recent massacres in Bosnia (1992–95, 225,000), Rwanda (1994, 700,000), and Darfur (2003–8, 373,000).¹⁵ The barely perceptible swelling from 2014 to 2016 includes the atrocities that contribute to the impression that we are living in newly violent times: at least 4,500 Yazidis, Christians, and Shiite civilians killed by ISIS; 5,000 killed by Boko Haram in Nigeria, Cameroon, and Chad; and 1,750 killed by Muslim and Christian militias in the Central African Republic.¹⁶ One can never use the word “fortunately” in connection with the killing of innocents, but the numbers in the 21st century are a fraction of those in earlier decades.

Of course, the numbers in a dataset cannot be interpreted as a direct readout of the underlying risk of war. The historical record is especially scanty when it comes to estimating any change in the likelihood of very rare but very destructive wars.¹⁷ To make sense of sparse data in a world whose history plays out only once, we need to supplement the numbers with knowledge about the generators of war, since, as the UNESCO motto notes, “Wars begin in the minds of men.” And indeed we find that the turn away from war consists in more than just a reduction in wars and war deaths; it also may be seen in nations’ preparations for war. The prevalence of conscription, the size of armed forces, and the level of global military spending as a percentage of GDP have all decreased in recent decades.¹⁸ Most important, there have been changes in the minds of men (and women).

How did it happen? The Age of Reason and the Enlightenment brought denunciations of war from Pascal, Swift, Voltaire, Samuel Johnson, and the Quakers, among others. It also saw practical suggestions for how to reduce or even eliminate war, particularly Kant’s famous essay “Perpetual Peace.”¹⁹ The spread of these ideas has been credited with the decline in great power wars in the 18th and 19th centuries and with several hiatuses in war during that interval.²⁰ But it was only after World War II that the pacifying forces identified by Kant and others were systematically put into place.

As we saw in chapter 1, many Enlightenment thinkers advanced the theory of gentle commerce, according to which international trade should make war less appealing. Sure enough, trade as a proportion of GDP shot up in the postwar era, and quantitative analyses have confirmed that trading countries are less likely to go to war, holding all else constant.²¹

Another brainchild of the Enlightenment is the theory that democratic government serves as a brake on glory-drunk leaders who would drag their countries into pointless wars. Starting in the 1970s, and accelerating after the fall of the Berlin Wall in 1989, more countries gave democracy a chance (chapter 14). While the categorical statement that no two democracies have ever gone to war is dubious, the data support a graded version of the Democratic Peace theory, in which pairs of countries that are more democratic are less likely to confront each other in militarized disputes.²²

The Long Peace was also helped along by some realpolitik. The massive destructive powers of the American and Soviet armies (even without their nuclear weapons) made the Cold War superpowers think twice about confronting each other on the battlefield—which, to the world’s surprise and relief, they never did.²³

Yet the biggest single change in the international order is an idea we seldom appreciate today: war is illegal. For most of history, that was not the case. Might made right, war was the continuation of policy by other means, and to the victor went the spoils. If one country felt it had been wronged by another, it could declare war, conquer some territory as compensation, and expect the annexation to be recognized by the rest of the world. The reason that Arizona, California, Colorado, Nevada, New Mexico, and Utah are American states is that in 1846 the United States conquered them from Mexico in a war over unpaid debts. That cannot happen today: the world’s nations have committed themselves to not waging war except in self-defense or with the approval of the United Nations Security Council. States are immortal, borders are grandfathered in, and any country that indulges in a war of conquest can expect opprobrium, not acquiescence, from the rest.