In How Europe Underdeveloped Africa (1972), Walter Rodney tells a complex story. He covers 500 years of history, beginning in the fifteenth century and reaching into the late twentieth century. Europe’s rise and Africa’s ruin are seen as parts of a single process of uneven development. It began with the Atlantic slave trade and the export of millions of people in their most productive years and turned local states into raiding machines. Farming was disrupted. And then the nineteenth century brought deindustrialization due to cheap imports of ironware and textiles, following the Industrial Revolution. The result, in Rodney’s terms, was “a gale-force wind, which shipwrecked a few societies, set many others off course, and generally slowed down the rate of advance” (p. 135). Then colonialism stopped progress entirely, according to Rodney. Surplus was extracted, industrialization deliberately blocked, African states dismantled, and “tribalism” encouraged because it allowed the Europeans to divide and rule. This is, then, a complex narrative with multiple causal channels that explain how Europe underdeveloped Africa.
Nathan Nunn’s analysis is, by contrast, far simpler. As Nunn explains in his 2005 PhD dissertation, he seeks to link “Africa’s history of extraction with its current level of development” (p. 112), inspired by Acemoglu, Johnson, and Robinson. His key contribution, published as an article in the Quarterly Journal of Economics in 2008, reports a negative correlation between the extent to which modern African countries had suffered due to the slave trade in the past and their current incomes per capita at the turn of the twenty-first century. The slave trade had, Nunn argued, underdeveloped Africa: everything that happened subsequently was of secondary importance.
By now, the fragility of this finding should be well-known. Ewout Frankema and Marlous van Waijenburg first demonstrated it in 2011, in a working paper for the Center for Global Economic History and the University of Utrecht, although their critique then disappeared from the version of the paper published in the Journal of Economic History. They demonstrated that there was no statistically significant negative correlation between Nunn’s estimates of slave exports per country (normalized to land area) and GDP per capita in either 1950 or 1960, with p < 0.10 only being achieved from 1970 up to 2000. Leticia Arroyo Abad and Noel Maurer then went further by updating the test to 2018. “Significance and coefficient size both rise in the 1960[s],” they note, “but in the 1990s the coefficient begins to shrink and p-values begin to rise. By 2018, the relationship has attenuated significantly” (p. 54). The pattern they observed can be seen replicated below, with the 95 percent confidence interval crossing the zero line from 2013 up to 2022. The magnitude and statistical significance of the effect Nunn found seems to depend on which year is used for GDP per capita.
Yet the critiques have largely ignored Nunn’s data construction, which is my speciality. According to his 2008 article, his country-level export numbers were produced by “combining data from ship records on the number of slaves shipped from each African port or region with data from a variety of historical documents that report the ethnic identities of slaves that were shipped from Africa” (p. 140). In doing so, he tried to bridge the gap between the data on the ports of embarkation and the places where people were actually captured and enslaved. For the Atlantic trade, Nunn reports using “54 different samples, totalling 80,656 slaves, with 229 distinct ethnic designations reported”; for the Indian Ocean, “six samples, with a total of 21,048 slaves and 80 different ethnicities reported”; for the Red Sea, two samples that “provide information for 67 slaves, with 32 different reported ethnicities”; for the Sahara, another two samples that “provide information on the origins of 5,385 slaves, with 23 different ethnicities recorded.” Using these samples, Nunn describes how he assigned the exports from each port to modern countries based on a variety of secondary sources that reveal where each ethnicity was located.
The problem is that the described methodology is based on a conceptual error.
