Our prehistory seems to have grown more bellicose as time went on, however. According to anthropologist Brian Ferguson, there is little or no clear-cut evidence of lethal group aggression among any societies prior to 12,000 years ago. War emerged and rapidly spread (PDF) over the next few thousand years among hunter-gatherers and other groups, particularly in regions where people abandoned a nomadic lifestyle for a more sedentary one and populations grew. War arose, according to this perspective, because of changing environmental and cultural conditions rather than because of "human nature," as the West Point War Museum suggests.
This view contradicts what many people believe about war. Since 2006, when I first started teaching a college course called "War and Human Nature," I've asked hundreds of students and other people whether humans will ever stop fighting wars. More than four in five—young and old, conservative and liberal, male and female—answer "No." Asked to explain this response, they often say that we have always fought wars, and we always will, because we are innately aggressive.
Of course, all human behavior ultimately stems from our biology. But the sudden emergence of war around 10,000 BCE and its recent decline suggest it's primarily a cultural phenomenon and one that culture is now helping us to overcome. There have been no international wars since the U.S. invasion of Iraq in 2003 and no wars between major industrialized powers since the end of World War II. Most conflicts now consist of guerilla wars, insurgencies, and terrorism—or what the political scientist John Mueller of Ohio State University calls the "remnants of war."
Mueller rejects biological explanations for this trend, noting in one paper (PDF) that "testosterone levels seem to be as high as ever." At least part of the decline, he says, can be attributed to a surge in the number of democracies since World War II, from 20 to nearly 100 (depending on how democracy is defined). Since democracies rarely, if ever, wage war against each other, we may well see a continuing decline in the magnitude of armed conflict.
Harvard psychologist Steven Pinker identifies several other cultural factors contributing to the modern decline of violence, both between and within states: First, the creation of stable states with effective legal systems and police forces has eliminated the endless feuding that plagued many tribal societies. Second, increased life expectancies make us less willing to risk our lives by engaging in violence. Third, as a result of globalization and communications, we have become increasingly interdependent on—and empathetic toward—others outside of our immediate "tribes."
If war is not inevitable, neither is peace. "This past year saw increasing threats to security, stability, and peace in nearly every corner of the globe," warns the SIPRI 2009 Yearbook. Global arms spending—especially by the United States, China, and Russia—has surged, and efforts to stem nuclear proliferation have stalled. An al-Qaida operative could detonate a nuclear suitcase bomb in New York City tomorrow, reversing the recent trend in an instant. But the evidence of a decline in war-related deaths shows that we need not—and should not—accept war as an eternal scourge of the human condition.
In fact, this fatalistic view is wrong empirically and morally. Empirically, because war clearly stems less from some hard-wired "instinct" than from mutable cultural and environmental conditions; much can be done, and has been done, to reduce the risks it poses. Morally, because the belief that war will never end helps perpetuate it. The surer we are that the world is irredeemably violent, the more likely we are to support hawkish leaders and policies, making our belief self-fulfilling. Our first step toward ending war is to believe that we can end it.