The Cold, Cold History of Political Conflict
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Jan 13, 2025

The Cold, Cold History of Political Conflict

Sustained temperature shifts during the “Little Ice Age” led to wars, mass migration, and instability. What does this mean for our current moment?

medieval farmers in a failing field watch an army march past.

Michael Meier

Based on the research of

Murat Iyigun

Joris Mueller

Nancy Qian

Summary In the period known as the Little Ice Age, from the early 14th century through the mid-19th century, widespread cooling resulted in drought, regional agricultural disruptions, and famines. Kellogg economist Nancy Qian and colleagues mapped this historic cooling alongside thousands of wars and battles that took place during the same period. This merged dataset revealed that when a region experienced cooling for more than 50 continuous years, that region also experienced an increase in wars and battles.

Earth’s climate has always been in flux. Over the centuries, for example, lands once lush with agriculture—like modern-day Jordan and large swaths of western China—have dried into mostly desert.

Throughout the ages, human societies similarly have been in flux, with recurring wars, human migration, and power shifts leading to the rise or fall of nation-states.

But to what extent are these through lines of human history—climate change and conflict—related to one another?

“Most of the time, we think of climate change as something very new, something we humans don’t know how to deal with,” says Nancy Qian, a professor of managerial economics and decision sciences at Kellogg. “But actually, the climate is always changing, and this interplay between climate and society, the economy, politics, and conflict is a story as old as time.”

To shed light on the historical relationship between climate change and political instability, Qian teamed up with Murat Iyigun of the University of Colorado Boulder and Joris Mueller of the University of Singapore. They analyzed the relationship between regional conflicts and regional changes in temperature and precipitation that occurred several hundred years ago during the so-called Little Ice Age.

The researchers’ analysis revealed that while sudden and acute cold shocks within a 50-year period were not associated with increased conflict, fighting did appear to escalate in regions that experienced two consecutive 50-year spells of cooling.

Human ingenuity may have allowed populations to successfully adapt to climate change over the short term (that is, fewer than 50 years), Qian says. But when climate change intensified and compounded over longer periods of time, societies were pushed into conflict.

“We need to appreciate that climate change is a very long process, and it can affect generations of people,” Qian says.

“Today’s climate change will be a complex and long-running process, with necessary economic changes, societal changes, cultural changes, and human migratory changes,” she adds. “We need to start thinking about that now.”

Climate clues in nature

Qian, Iyigun, and Mueller focused their research on the Little Ice Age, a period of widespread cooling from the early 14th century through the mid-19th century that was especially pronounced in areas around the northern part of the Atlantic Ocean.

Significant cooling during this period expanded the footprints of glaciers and froze seas as far south as modern-day Turkey. The temperature shifts also led to increased variability in precipitation. This in turn resulted in drought, regional agricultural disruptions, and famines, which weakened states and opened the door to conflict and invasion.

“If you only have problems for a few years, those problems are easily moderated. But if you have generations of distress, those divisions get deeper and deeper, and they’re very hard to get out of.”

Nancy Qian

For their study, Qian and colleagues created a dataset of wars and battles fought between 1400 and 1900 in Europe, the Near East, and Northern Africa. Their final sample included 2,792 skirmishes. The researchers merged this dataset with historical climate data that was constructed by geologists and climatologists using subtle clues from nature, like tree rings and fossilized pollen, as well as written documentation of weather events recorded by the period’s travelers and traders.

The research team then divided the region into 400-kilometer-by-400-kilometer cells on a grid, and plotted the conflicts and climate shifts onto their corresponding locations to see what patterns might emerge.

Compounding challenges

When a cell of land experienced two consecutive periods of cooling, its incidence of conflict jumped by 3.86 percent, the researchers found. Moreover, places heavily reliant on agriculture were more likely to see fighting between 1401 and 1450, as were cells where two different territories or states shared a border. Reliance on agriculture and proximity to other groups appears to have primed these regions for political instability, making them more susceptible to conflict as weather changes continued.

“Our interpretation is that the conflicts were compounding,” Qian says. She surmises that as the weather cooled, and a society’s usual agricultural practices lost viability, the society adapted and looked to new approaches. But if the climate change persisted for longer than five decades or so, society may have had to consider more desperate and disruptive adaptations—perhaps involving migration or fighting for resources.

It wasn’t simply that there was a specific threshold for low temperature at which food provision became impossible, according to Qian. The researchers ruled out that possible explanation by controlling for temperature level in their study. Qian believes that, instead, what explains the spike in fighting is the stress of having to repeatedly find new ways to cope with an increasingly colder life.

After all, even today we can see how decades of conflict (not necessarily related to climate change) are reshaping societies and cultures.

“If you only have problems for a few years, those problems are easily moderated,” she says. “But if you have generations of distress, those divisions get deeper and deeper, and they’re very hard to get out of.”

Better future-casting

Qian is hopeful that, as technology and available datasets continue to improve, researchers will be able to form a more detailed understanding of how climate change has historically shaped society—and how it might do so in the future. This type of research could help establish key strategies for ameliorating the negative impacts of a changing climate on society.

“When we look at countries on the front lines of climate change—particularly the ones that don’t have the economic resources of the U.S. or Northern Europe—we hear about many possible solutions, from improving education to gender equality,” Qian says. Though those approaches are important, “they sidestep the fundamental issue: many people today no longer have land that produces food. They will remain poor, and they will continue to fight, until this can be addressed.”

Featured Faculty

James J. O'Connor Professor of Managerial Economics & Decision Sciences

About the Writer

Katie Gilbert is a freelance writer in Philadelphia.

About the Research

Iyigun, Murat, Joris Mueller, and Nancy Qian. 2024. “The Intensifying Effects of Prolonged Climate Change on Conflict, 1400-1900 CE.” AEA Papers and Proceedings.m

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