War! (Huh!) What is it good for? The expansion of empires and the proliferation of complex social structures and institutions, potentially! OK, that might not make for a particularly catchy song, but it does summarize an intriguing new study in the journal Science Advances, which suggests that warfare may have been a bigger driver of social complexity than agriculture.

Since the start of the Holocene roughly 10,000 years ago, stable global temperatures have allowed for reliable crop yields, enabling us humans to ditch the nomadic drifter vibe and settle down in permanent agricultural settlements. This, in turn, has led to the division of labor and the development of increasingly complex societies, triggering our evolution from hunter-gatherers to farmers to space travel sniffer people.

Unfortunately, however, human history consists of more than just watermelons and sunflowers, and it’s a tragic fact that conflict has also shaped our trajectory as a species. To test the role of warfare in the emergence of complex societies, the study authors tapped into the Seshat: Global History Databank, which consists of historians, archaeologists, and other experts on past civilizations around the world over the past ten millennia.

After consulting with these scholars, the researchers identified 17 different variables that influence sociopolitical complexity and devised an algorithm to determine which of these is the biggest driver of this process. Summarizing their findings, the authors write that “this analysis identified an unexpectedly simple web of causation, in which the chief drivers of increasing social complexity and scale are agriculture and warfare.”

Breaking the data down further, they explain that the advent of two military technologies – namely iron weapons and cavalries – appear to eclipse all other factors as the greatest facilitators of social complexity. For instance, they explain that the first macrostates – defined as polities controlling a territory greater than 100,000 square kilometers (~38,600 square miles) – arose in Mesopotamia and Egypt following the spread of bronze metallurgy.

When bronze weapons were later combined with the use of armies mounted on horseback, “very large empires” covering more than 3 million square kilometers (~1.2 million square miles) became possible for the first time. Significantly, the authors note that “in each of the major Eurasian subregions, these megaempires arose three or four centuries following the appearance of cavalry.”

This may sound like quite a long delay, but the researchers insist that “innovations in military technology resulted in more rapid evolutionary change, compared to the adoption of agriculture.”

It’s important to note, however, that this study relies on a specific definition of social complexity and does not suggest that warfare has helped to spur cultural complexity in human societies. Rather, the authors find that military technologies have triggered the expansion of three specific aspects of civilization – these being the size of the territory occupied by a society, the intricacy of the ruling hierarchy, and the emergence of specialized bureaucratic and legal institutions.

Back to the data, and it appears that the maximum territory held by major empires remained roughly stable for two millennia following the “IronCav revolution”. It would require another military milestone, the “Gunpowder Revolution”, for this social complexity threshold to be broken. 

Tellingly, the study authors note that “the time lag between the appearance of effective gunpowder weapons and the rise of European colonial empires was also 300 to 400 years,” highlighting a repeating pattern whereby military innovation seemingly begets the expansion of human civilization.

Wrapping up their report, the researchers explain that this analysis is far from comprehensive and that more in-depth studies into different aspects of social complexity are required in order to determine the true importance of warfare. 

Yet, if these initial findings are anything to go by, it would seem that the dagger may be more powerful than the cabbage when it comes to shaping human history.