How the Potato Ushered in an Era of Peace
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Economics Social Impact May 2, 2018

How the Pota­to Ush­ered in an Era of Peace

Its arrival in Europe had con­se­quences that went far beyond diet.

A man picks potatoes, which helped bring peace

Lisa Röper

Based on the research of

Murat Iyigun

Nathan Nunn

Nancy Qian

The pota­to, small and hum­ble though it may be, has played an out­sized role in history. 

Many schol­ars cred­it the hardy and nutri­ent-rich crop with rapid pop­u­la­tion growth across Europe; the tuber has been linked to the rise of indus­tri­al­iza­tion and empire in the West, and in the mid-19th cen­tu­ry, the col­lapse of Ireland’s pota­to crop drove a wave of immi­gra­tion to the Unit­ed States, for­ev­er chang­ing the young country. 

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Now, the pota­to can add a new line to its already fas­ci­nat­ing resume: peacemaker.

Research from Nan­cy Qian, a pro­fes­sor of man­age­r­i­al eco­nom­ics and deci­sion sci­ences at the Kel­logg School, finds that pota­toes, and the per­ma­nent boost in agri­cul­tur­al pro­duc­tiv­i­ty they brought about, reduced glob­al armed con­flict in the 18th and 19th centuries. 

Pota­toes became cul­ti­vat­ed as a crop in Europe around 1700, at which point the regions that could grow pota­toes expe­ri­enced a sharp decline in con­flict that last­ed for the next 200 years,” Qian says. 

Qian and her coau­thors exam­ined armed con­flict in Europe, North Africa, and the Mid­dle East between 1400 and 1900 — a noto­ri­ous­ly bloody and bru­tal peri­od. Every­one was fight­ing every­one, all the time,” she says.

But things changed when Span­ish explor­ers brought back the pota­to from South Amer­i­ca in the 16th cen­tu­ry, her study shows. Sud­den­ly, a fam­i­ly of four could grow enough food to sur­vive on about a third as much land as they need­ed before. In fact, a diet of only pota­toes, sup­ple­ment­ed by dairy, pro­vides all the vit­a­mins humans need. 

These his­tor­i­cal jumps in agri­cul­tur­al pro­duc­tiv­i­ty alter the land­scape of human civ­i­liza­tion in impor­tant and fun­da­men­tal ways we haven’t real­ly talked about.” 

This abrupt change in the food sup­ply was enough to prompt bat­tle-hard­ened Euro­peans to put down their weapons. 

Qian can’t say for sure exact­ly why peo­ple swapped the sword for the spud, but she has a strong suspicion. 

His­tor­i­cal­ly, agri­cul­tur­al land was the most valu­able resource,” she explains. If the land is able to pro­duce more food per area, then it becomes cheap­er — and if it’s cheap­er, then it’s less valu­able, and peo­ple don’t want to fight over it as much.” 

She thinks it’s also pos­si­ble farm­ers found the prospect of going to bat­tle less entic­ing when they had a suc­cess­ful har­vest to man­age at home. But what­ev­er the mech­a­nism, it is clear that pota­toes ush­ered in a more peace­ful era. 

Spuds and Stats

In a 2011 paper, Qian and coau­thor Nathan Nunn at Har­vard found that pota­toes were respon­si­ble for a sig­nif­i­cant por­tion of the increase in pop­u­la­tion and urban­iza­tion that took place in the West in the 18th and 19th centuries. 

She began to won­der what else might have changed after pota­toes arrived in the Old World, fig­ur­ing if you’ve got all this food, that’s got to be good for oth­er stuff,” she says. 

So Qian and Nunn teamed up with Murat Iyi­gun at the Uni­ver­si­ty of Col­orado to inves­ti­gate the rela­tion­ship between pota­toes and con­flict. They decid­ed to focus on spe­cif­ic bat­tles instead of wars, for a vari­ety of rea­sons: it is not always clear from the his­tor­i­cal record when a par­tic­u­lar war began or end­ed, and in some cas­es, it can be chal­leng­ing to decide to which wars bat­tles belonged. 


A couple on a potato farm, which helped bring peace.
Lisa Röper

To do this they need­ed to assem­ble a com­pre­hen­sive, five-cen­tu­ry data­base of armed con­flict in Europe, North Africa, and the Mid­dle East — a task the researchers thought might take six months. The team labo­ri­ous­ly dig­i­tized data from sev­er­al bat­tle ency­clo­pe­dias com­piled by his­to­ri­ans. It took six years. 

They cre­at­ed a dataset of all Euro­pean bat­tles from 1400 onward in which 32 or more com­bat fatal­i­ties occurred. The dataset includes the name, time, and loca­tion of each skir­mish, and infor­ma­tion about the par­ties involved in it. This infor­ma­tion allowed them to plot each bat­tle on a map. 

Then, they divid­ed that map into 400 km by 400 km squares (each about a third the size of mod­ern-day France), not­ing which squares were suit­able for grow­ing pota­toes and which were not. 

Did grids with cli­mates suit­able for grow­ing pota­toes see a decrease in con­flict after 1700, as com­pared to grids with cli­mates unsuit­able for grow­ing potatoes? 

Indeed they did, the researchers dis­cov­ered. If you can cul­ti­vate pota­toes, then after they become avail­able, you expe­ri­ence a decline in con­flict, rel­a­tive to grids that can­not cul­ti­vate pota­toes,” Qian explains. In fact, 26 per­cent of the vari­a­tion in con­flict is explained by the vari­a­tion in pota­to cultivation. 

But a ques­tion sprout­ed up: How could the researchers be sure that pota­toes were actu­al­ly reduc­ing con­flict, as opposed to export­ing con­flict else­where? In oth­er words, per­haps pota­to-rich regions were not fight­ing at home, as they once did, but were instead pick­ing fights in areas that could not pro­duce potatoes. 

To rule out this pos­si­bil­i­ty, the researchers exclud­ed from their analy­sis any bat­tles in which the two actors were locat­ed very far from each oth­er. In the end, even when they lim­it­ed their analy­sis to local and civ­il con­flict, the results held true. 

This abrupt change in the food sup­ply was enough to prompt bat­tle-hard­ened Euro­peans to put down their weapons.

They also want­ed to make sure that pota­to-friend­ly regions did not have oth­er unre­lat­ed advan­tages that might have brought about a decrease in con­flict. So they con­trolled for a vari­ety of poten­tial­ly con­found­ing fac­tors, includ­ing weath­er shocks such as sud­den increas­es or decreas­es in rain­fall; geo­graph­ic char­ac­ter­is­tics such as ele­va­tion and rugged­ness; and suit­abil­i­ty to grow oth­er sta­ple crops intro­duced from the Columbian exchange, such as maize and sweet potatoes. 

This allowed them to con­firm that it was pota­toes, and only pota­toes, that were respon­si­ble for the change. 

How Pota­toes Changed His­to­ry

Until recent­ly, Qian says, his­to­ri­ans and econ­o­mists did not have much evi­dence of how increas­ing agri­cul­tur­al pro­duc­tiv­i­ty shaped the world over the long run — some­thing she felt was an over­sight. For most of human his­to­ry, land was the most impor­tant resource, and cul­ti­vat­ing crops was a life-and-death affair. But after 1700, the food sup­ply was sud­den­ly more abun­dant and sta­ble than it had ever been. 

That shift, her research shows, brought about oth­er mon­u­men­tal changes: The glob­al pop­u­la­tion increased. Cities grew. Con­flict lessened. 

These his­tor­i­cal jumps in agri­cul­tur­al pro­duc­tiv­i­ty alter the land­scape of human civ­i­liza­tion in impor­tant and fun­da­men­tal ways we haven’t real­ly talked about,” Qian says. 

Although her research shows pota­toes were a boon for the world, there is one impor­tant place where they have not reduced con­flict: Qian’s own kitchen. Despite hav­ing writ­ten two research papers about them, she admits she does not par­tic­u­lar­ly like pota­toes. Her hus­band, whose native Belarus has the high­est per-capi­ta pota­to con­sump­tion of any coun­try in the world, loves them. 

He’s always try­ing to get me to cook more pota­toes,” she says. And he tries to use these papers against me: You show they’re real­ly good for every­thing, so we should cook more potatoes.’” 

Featured Faculty

Nancy Qian

Professor of Managerial Economics & Decision Sciences

About the Writer

Susie Allen is a freelance writer in Chicago.

About the Research

Iyigun, Murat, Nathan Nunn, and Nancy Qian. 2017. “The Long-Run Effects of Agricultural Productivity on Conflict.” Working paper.

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