People have been killing each other since as long as there have been people. Yet organized warfare appears not to have sprung up until the Neolithic Age, when certain societies began farming and living in permanent settlements. Archaeological evidence suggests that Neolithic warfare progressed from small-scale clashes and massacres to longer and more sophisticated conflicts.

Early humans engaged in warfare in only the very broadest sense. “For most of our species’ history, it would have been very small, unorganized, decentralized raids very similar to what you see in chimpanzees,” says Luke Glowacki, an assistant professor of anthropology at Boston University, and an expert on the evolution of war. During this time, he says, “a group of individuals [might] encounter someone from another group and kill them.”

Roughly 12,000 years ago, agriculture emerged in the Fertile Crescent, and population densities increased even in areas without crops. “Agriculture is not required” for warfare, Glowacki says, “but it certainly does facilitate it.”

To date, researchers have found no definitive evidence that organized warfare pre-dates the so-called Neolithic Revolution. Basic warfare, however, is known to have broken out soon after. A 2016 study, for example, concluded that a massacre took place some 10,000 years ago near Lake Turkana in Kenya, with the victims showing signs of bound hands, arrow wounds and fractured skulls.

“I consider this to be the most reliable early evidence of a massacre,” says Glowacki, who was not involved in the study. “These are hunter-gatherers, but with some food storage and likely lower mobility.” He points out that massacres require more coordination and planning than “tit-for-tat raiding,” that they’re “indicative of more severe war,” and that they tend to occur when humans transition from mobile to sedentary lifestyles.

In present-day Germany, a massacre took place some 7,000 years ago, when attackers apparently tortured their victims—in part by breaking their shin bones—prior to killing them. Similar Neolithic massacres have been uncovered elsewhere in Germany and Austria, as well as in Croatia and France. Meanwhile, the inhabitants of Jericho, among the oldest cities in the world, built city walls around 8000 B.C., seemingly to keep out invaders.

As noted in a November 2023 study in the journal Scientific Reports, such Neolithic conflicts were presumed to be a “mixture of rapid assaults or short raids, generally lasting no more than a few days and affecting no more than 20 or 30 individuals.”

As it turns out, though, at least some later Neolithic fighting may have been more complex than previously realized, according to the study, which analyzed the skeletal remains of 338 individuals who died in northern Spain 5,400 to 5,000 years ago.

These remains, accidentally unearthed by a bulldozer in 1985, were originally believed to constitute another Neolithic massacre. Yet by looking closer at the skeletal injuries—which disproportionately affected males and were largely non-fatal (something not observed at other Neolithic mass-fatality sites in Europe)—the study’s authors determined that a protracted struggle had lasted months or years.

“We think we are seeing the result of a regional inter-group conflict,” lead author Teresa Fernández-Crespo, an archaeologist at the University of Valladolid in Spain, tells HISTORY in an email. She adds that “resource competition and social complexity could have been a source of tension, potentially escalating into lethal violence.”

As the Neolithic progressed, advances in agriculture may have gone hand-in-hand with advances in warfare. “Because they had to cooperate to irrigate the land, the idea of working together and cooperating also gave rise to armies,” says Alfred S. Bradford, chair in ancient history at the University of Oklahoma, and author of With Arrow, Sword, and Spear__: A History of Warfare in the Ancient World. “And, of course, they had a lot to defend because they were defending their farmland.”

Copper tools and weapons began to replace stone arrowheads, spear tips, blades and axes in the Middle East and elsewhere. By the time the Bronze Age arrived around 3300 B.C., early civilizations in Mesopotamia and North Africa had developed large armies with formal leaders, chains of command, distinct units and supply systems. These civilizations, literate and artistically inclined, could document their military campaigns.

The so-called Standard of Ur, for instance, depicts an advancing Sumerian army, with wheeled wagons and infantry, from around 2500 B.C., whereas the Narmer Palette highlights an Egyptian conquest from around 3000 B.C.

Outside of Greece, large-scale combat took longer to arrive in Europe. But by around 1200 B.C. a battle along the Tollense River in Germany involved perhaps 4,000 combatants. Armies likewise developed in places like Peru, Mexico and China. Throughout the world, warfare had begun to resemble what it is today.