The slave trade in sub-Saharan Africa between 1400 and 1900 contributes to political violence to this day, particularly in areas with less economic development and those with a weaker national identity resulting from colonial rule, a new study has shown. 

Researchers looked at the pre-colonial ancestral homelands of 638 ethnic groups across 35 present-day sub-Saharan African countries between 1997 and 2016. Some of the groups' historical lands fell over current national borders, so the researchers ultimately counted 907 country-ethnic groups. 

In their analysis, published March 15 in the Journal of Comparative Economics, researchers found that the 412 regions that were home to ethnic groups whose members were taken away and enslaved had more political violence. The mean value of political violence intensity, measured using the total number of political violence incidents between 1997 and 2016, was 18.4% higher in those 412 regions than it was in the 495 regions that were not directly involved in the slave trade.

Zhicheng Phil Xu, a co-author and an associate professor at Henan University's School of Economics, said the findings have policy implications for African nations and point to the terrible ongoing damage wrought by foreign powers, including the U.S., whose economy was built by enslaved people, and the U.K., which amassed enormous wealth through the transport and enslavement of more than 3 million African people. 

"We believe our efforts to build a peaceful and prosperous Africa are our academic and moral responsibility," Xu said. The professor formerly worked at Texas A&M University's Center on Conflict and Development; another co-author, Shahriar Kibriya, is the associate director of the center.

Drawing on previous research about the slave trade and the backgrounds of enslaved African people by the economists Leonard Wantchekon and Nathan Nunn, the researchers measured the intensity of the slave trade by taking the number of people removed from their homes through the transatlantic and Indian Ocean slave trade routes between 1400 and 1900 and accounting for the area of each ethnic group's lands. The study took the more contemporary violence data from the Armed Conflict Location & Event Data Project, or ACLED, on five categories of political violence — civil conflict, riot, political militia conflict, violence against civilians and ethnic conflict — which Xu said generally did not overlap.

To retest the findings, the researchers examined whether a country-ethnic region's distance from the coast was correlated with contemporary political violence — a predictor of slave trade exploitation but apparently unrelated to any current-day contributors to violence — and found similar results. When they dropped all landlocked countries in the sample, the result was, again, significant. They also controlled for geographic features such as land area, access to rivers, elevation and latitude; natural resource characteristics such as the occurrence of precious metals, diamonds and petroleum; temperature and precipitation; and the length of an ethnic region's border with one or more other ethnic regions.

Regions where people were formerly treated like chattel were particularly vulnerable to riot and ethnic conflict, the study found. But both of those types of conflict were significantly mediated by present-day conditions. When the model accounted for greater economic development as measured by density of lighting at night, the researchers' riot estimate went down 24%, while ethnic conflict went down only 9%. 

Weak national identity, as measured in the pan-Africa Afrobarometer survey, seemed to explain some of the researchers' findings of ethnic conflict: Stronger national identity was correlated with less violence. Likewise, people whose ancestors were "heavily threatened" during the slave trade had "a greater propensity to report a strong sense of ethnic identity rather than national identity," the authors wrote.

Xu told The Academic Times that African nations could use the findings to tailor their own policies. 

"Significant reductions in ethnic conflict could be obtained by encouraging policies that strengthen social consensus and shared identity, even in the context of relatively weak governance," Xu said. "For example, ethnic identity is not allowed to be shown in the ID card in Tanzania and Rwanda. This policy is proven to be effective to strengthen national identity. We believe education on the nation's history could be also effective."

The study, "The long-term effects of the slave trade on political violence in Sub-Saharan Africa," was published March 15 in the Journal of Comparative Economics, was authored by Yu Zhang, Nanjing Audit University; Zhicheng Phil Xu, Henan University; and Shahriar Kibriya, Texas A&M University.