SOLUTION: UCSD Slave Trade Negative Effect on Africas Development & Economy Paper Discussion

Africa’s economic performance in the second half of the twentieth century has been poor. One, often informal, explanation for
Africa’s underdevelopment is its history of extraction, characterized by two events: the slave trades and colonialism. Bairoch
(1993, p. 8) writes that “there is no doubt that a large number
of negative structural features of the process of economic underdevelopment have historical roots going back to European colonization.” Manning (1990, p. 124) echoes Bairoch but focuses
on the slave trades, writing, “Slavery was corruption: it involved
theft, bribery, and exercise of brute force as well as ruses. Slavery
thus may be seen as one source of precolonial origins for modern
Recent empirical studies suggest that Africa’s history can
explain part of its current underdevelopment. These studies focus on the link between countries’ colonial experience and current economic development (Grier 1999; Englebert 2000a, 2000b;
* A previous version of this paper was circulated under the title “Slavery, Institutional Development, and Long-Run Growth in Africa.” I am grateful to the editor,
Edward Glaeser, and three anonymous referees for comments that substantially
improved this paper. I also thank Daron Acemoglu, Robert Bates, Albert Berry,
Loren Brandt, Jon Cohen, Bill Easterly, Stanley Engerman, Azim Essaji, Joseph
Inikori, Martin Klein, Pat Manning, Ted Miguel, Jim Robinson, Aloysius Siow, Ken
Sokoloff, Dan Trefler, Chris Udry, Jeffrey Williamson, and seminar participants
at the University of British Columbia, the University of California Los Angeles,
the University of California San Diego, Harvard University, the University of
Michigan, New York University, Pennsylvania State University, the University of
Rochester, the University of Southern California, the University of Toronto, York
University, the CIFAR, the SED Conference, the CEA Meetings, the SSHA Meetings, the ITAM Summer Camp in Macroeconomics, the IEHC, the NBER, and the
WGAPE meetings for valuable comments and suggestions. I thank Maira Avila
and Ken Jackson for excellent research assistance.
C 2008 by the President and Fellows of Harvard College and the Massachusetts Institute of

The Quarterly Journal of Economics, February 2008
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Can part of Africa’s current underdevelopment be explained by its slave
trades? To explore this question, I use data from shipping records and historical documents reporting slave ethnicities to construct estimates of the number
of slaves exported from each country during Africa’s slave trades. I find a robust
negative relationship between the number of slaves exported from a country and
current economic performance. To better understand if the relationship is causal,
I examine the historical evidence on selection into the slave trades and use instrumental variables. Together the evidence suggests that the slave trades had an
adverse effect on economic development.
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Acemoglu, Johnson, and Robinson 2001, 2002; Bertocchi and
Canova 2002; Lange 2004). However, the other important event
in Africa’s history, its slave trades, has yet to be examined empirically. There are reasons to expect that the slave trades may have
been at least as important as official colonial rule for Africa’s development. For a period of nearly 500 years, from 1400 to 1900, the
African continent simultaneously experienced four slave trades.
By comparison, official colonial rule lasted from 1885 to about
1960, a total of approximately 75 years.
This paper provides the first empirical examination of the importance of Africa’s slave trades in shaping subsequent economic
development. In doing this, I construct measures of the number
of slaves exported from each country in Africa in each century between 1400 and 1900. The estimates are constructed 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. I find a robust negative relationship between
the number of slaves exported from each country and subsequent
economic performance. The African countries that are the poorest
today are the ones from which the most slaves were taken.
This finding cannot be taken as conclusive evidence that the
slave trades caused differences in subsequent economic development. An alternative explanation that is just as plausible is that
countries that were initially the most economically and socially
underdeveloped selected into the slave trades, and these countries
continue to be the most underdeveloped today. In other words, the
slave trades may be correlated with unobserved country characteristics, resulting in biased estimates of the effect of the slave
trades on economic development.
I pursue a number of strategies to better understand the reason behind the relationship between slave exports and current
economic performance. First, I review the evidence from African
historians on the nature of selection into the slave trades. I also
use historic data on pre–slave trade population densities to examine whether it was the less developed parts of Africa that selected
into the slave trades. Both sources of evidence show that it was
actually the most developed areas of Africa that tended to select
into the slave trades. I discuss the reason behind this seemingly
paradoxical relationship in detail. Second, I use instruments to
estimate the causal effect of the slave trades on subsequent economic development. The instruments are the sailing distances
Between 1400 and 1900, the African continent experienced
four simultaneous slave trades. The largest and most well-known
is the trans-Atlantic slave trade where, beginning in the fifteenth
century, slaves were shipped from West Africa, West-Central
Africa, and Eastern Africa to the European colonies in the New
World. The three other slave trades—the trans-Saharan, Red Sea,
and Indian Ocean slave trades—were much older and pre-dated
the trans-Atlantic slave trade. During the trans-Saharan slave
trade, slaves were taken from south of the Saharan desert to
1. Also see Lagerlöf (2005) and Mitchener and McLean (2003) for related
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from each country to the nearest locations of demand for slave
labor in each of the four slave trades. Like the OLS coefficients,
the IV coefficients are negative and significant, suggesting that
increased extraction during the slave trades caused worse subsequent economic performance.
I then explore the precise channel of causality underlying the
relationship between slave exports and economic development.
Using historical evidence as a guide, I examine whether the procurement of slaves through internal warfare, raiding, and kidnapping resulted in subsequent state collapse and ethnic fractionalization. I find that the data are consistent with these channels.
These findings complement the research of Engerman and
Sokoloff (1997, 2002), which shows that slavery in the New World
resulted in the evolution of institutions that were not conducive
to economic growth.1 My results show that not only was the use of
slaves detrimental for a society, but the production of slaves, which
occurred through domestic warfare, raiding, and kidnapping, also
had negative impacts on subsequent development.
The paper is structured as follows. In the following section, I
provide a description of Africa’s slave trades, providing a detailed
historical overview of the manner in which slaves were procured
and the resulting adverse effects. In Section III, I describe the
construction of the slave export figures. Section IV documents
the correlations that exist in the data, and Section V turns to
the issue of causality. In Section VI, guided by the historical evidence, I examine the potential channels of causality. Section VII
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Northern Africa. In the Red Sea slave trade, slaves were taken
from inland of the Red Sea and shipped to the Middle East and
India. In the Indian Ocean slave trade, slaves were taken from
Eastern Africa and shipped either to the Middle East and India
or to plantation islands in the Indian Ocean.
A number of characteristics of Africa’s slave trades make
them distinct from previous slave trades. First, the total volume
of slaves traded was unprecedented. During the trans-Atlantic
slave trade alone, approximately 12 million slaves were exported
from Africa. Another 6 million were exported in the other three
slave trades. These figures do not include those who were killed
during the raids or those who died on their journey to the coast.
The total effect of the slave trades, according to calculations by
Patrick Manning (1990, p. 171), was that by 1850 Africa’s population was only half of what it would have been had the slave trades
not taken place.
Africa’s slave trades were also unique because, unlike previous slave trades, individuals of the same or similar ethnicities
enslaved one another. This had particularly detrimental consequences, including social and ethnic fragmentation, political instability and a weakening of states, and the corruption of judicial
The most common manner in which slaves were taken was
through villages or states raiding one another (Northrup 1978;
Lovejoy 1994). Where groups of villages had previously developed
into larger-scale village federations, relations between the villages
tended to turn hostile (e.g., Azevedo 1982; Inikori 2000; Hubbell
2001). As a result, ties between villages were weakened, which in
turn impeded the formation of larger communities and broader
ethnic identities. Kusimba (2004, p. 66) writes that “insecurity
confined people within ethnic boundaries constructing spheres of
interaction.” Because of this process, the slave trades may be an
important factor explaining Africa’s high level of ethnic fractionalization today. This is significant for economic development given
the established relationship between ethnic fractionalization and
long-term economic growth (Easterly and Levine 1997).
Because of the environment of uncertainty and insecurity
at the time, individuals required weapons, such as iron knives,
spears, swords or firearms, to defend themselves. These weapons
could be obtained from Europeans in exchange for slaves, who
were often obtained through local kidnappings. This further
perpetuated the slave trade and the insecurity that it caused,
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which in turn further increased the need to enslave others to
protect oneself (Mahadi 1992; Hawthorne 1999, pp. 108–109).
Historians have named this vicious cycle the “gun–slave cycle”
(e.g., Lovejoy 2000) or the “iron–slave cycle” (e.g., Hawthorne
2003). The result of this vicious cycle was not only that communities raided other communities for slaves, but also that members of
a community raided and kidnapped others within the community.
Well-documented examples come from the Balanta of modern day
Guinea-Bissau, the Minyanka of modern day Mali (Klein 2001),
and the Makua, Chikunda, and Yao of East Central Africa (Alpers
1969, pp. 413–414, 1975, p. 225; Isaacman 1989, pp. 191–192, 196).
Generally, the consequence of internal conflict was increased
political instability and in many cases the collapse of preexisting forms of government (Lovejoy 2000, pp. 68–70). In sixteenthcentury northern Senegambia, the Portuguese slave trade was a
key factor leading to the eventual disintegration of the Joloff Confederation, which was replaced by the much smaller kingdoms of
Waalo, Kajoor, Baol, Siin, and Saalum. Further south, in southern Senegambia, the same pattern is observed. Prior to the slave
trades, complex state systems were in the process of evolving.
However, this evolution stagnated soon after the arrival of the
Portuguese in the 15th century (Barry 1998, pp. 36–59). Similar patterns of instability have also been documented in Eastern Africa (e.g., Isaacman [1989]; Mbajedwe [2000]). In the late
19th century, the slave trades resulted in the disintegration of the
Shambaa kingdom, the Gweno kingdom, and the Pare states in
East Africa’s Pangani valley (Kimambo 1989, p. 247; Mbajedwe
2000, pp. 341–342).
The most dramatic example may be the Kongo kingdom of
West-Central Africa. As early as 1514, the kidnapping of local Kongo citizens for sale to the Portuguese had become rampant, threatening social order and the King’s authority. In 1526,
Affonso, king of Kongo, wrote to Portugal complaining that “there
are many traders in all corners of the country. They bring ruin to
the country. Every day people are enslaved and kidnapped, even
nobles, even members of the king’s own family” (Vansina 1966,
p. 52). This break-down of law and order was partly responsible
for the weakening and eventual fall of the once powerful state
(Inikori 2003). For many of the other Bantu-speaking ethnicities,
stable states also existed in earlier periods, but by the time the
slave trades were brought to an end, few ancient states remained
(Colson 1969, pp. 36–37).
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Preexisting governance structures were generally replaced by
small bands of slave raiders, controlled by an established ruler or
warlord. However, these bands were generally unable to develop
into large, stable states. Colson (1969, p. 35) writes that “both
the bands and the new states they created retained an air of
improvisation. Few band leaders were able to hand power to a
legitimate successor. Even where a band leader had become the
ruler of a state, succession remained a problem. Leadership was
a personal role, rather than an established office.”
The slave trades also contributed to political instability by
causing the corruption of previously established legal structures.
In many cases, it became common to obtain slaves by falsely accusing others of witchcraft or other crimes (Koelle 1854; Northrup
1978; Lovejoy 2000). Klein (2001, p. 59) writes that “communities
began enslaving their own. Judicial penalties that formerly had
taken the form of beatings, payment of compensation or exile,
for example, were now converted to enslavement.” Often, leaders
themselves supported or even instigated this abuse of the judicial system (Mahadi 1992; Hawthorne 1999, 2003; Klein 2001).
To protect themselves and their communities from being raided,
leaders often chose to pay slaves as tribute, which were often
obtained through the judicial system. Hawthorne (1999, 2003)
provides detailed studies of this process among the Cassanga of
modern day Guinea Bissau. The chief of the Cassanga used the
“red water ordeal” to procure slaves and their possessions. Those
accused of a crime were forced to drink a poisonous red liquid. If
they vomited, then they were judged to be guilty. If they did not
vomit, they were deemed not guilty. However, for those that did
not vomit this usually brought death by poisoning. Their possessions were then seized and their family members were sold into
Evidence from research showing a relationship between a
country’s history of state development and subsequent economic
performance suggests that these effects of the slave trades may be
important for current economic development (Bockstette, Chanda,
and Putterman 2002; Chanda and Putterman 2005). Others have
argued that Africa’s underdevelopment is a direct result of state
failure, which stems from Africa’s weak and unstable precolonial
political structures (Herbst 1997, 2000). Because Africa’s slave
trades were an important factor affecting political underdevelopment, they may be a central reason behind Africa’s weak states
2. Ideally, I would also like to include people that entered into local domestic
slavery. However, the necessary data to construct these estimates do not exist.
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Because I am interested in examining the effects of the slave
trades that resulted because of the procurement of slaves, my
measure of interest is the total number of slaves taken from
each country during the four slave trades between 1400 and
I use two types of data to construct the slave export estimates. The first are data that report the total number of slaves
exported from each port or region in Africa. I refer to these as shipping data. For the trans-Atlantic slave trade, the data are from
the updated version of the Trans-Atlantic Slave Trade Database
constructed by Eltis et al. (1999). The database records information for 34,584 voyages from 1514 to 1866. The shipping data are
originally from various documents and records located around
the world. Because, in most European ports, merchants were required to register their ships and declare the volume and value of
goods transported for each ship and voyage, typically, there exists
a number of different registers and documents. In the database,
77% of the trans-Atlantic slave voyages after 1700 have shipping
information from more than one source; the average number of
sources for each voyage is six. It is estimated that the database
contains 82% of all trans-Atlantic slaving voyages ever attempted
(Eltis and Richardson 2006).
Data for the early period of the Atlantic slave trade not covered by the Trans-Atlantic Slave Trade Database are from Elbl
(1997). For the Indian Ocean, Red Sea, and trans-Saharan slave
trades, data are from Austen (1979, 1988, 1992). The data are
based on estimates from all available documents, records, and accounts by observers and government officials on the location and
volume of slave exports.
With the shipping data one can calculate the number of slaves
that were shipped from each coastal country. However, this does
not give an accurate indication of where slaves were originally
captured. Slaves shipped from the ports of a coastal country may
have come from a country located further inland. To estimate the
number of slaves shipped from the coast that came from inland
countries, I also use a second source of data that reports the ethnic
identity of slaves shipped from Africa. This information comes
from a variety of sources, such as records of sale, slave registers,
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slave runaway notices, court records, church records, and notarial
There were a number of ways of identifying the ethnicity
or “nation” of a slave. The easiest was often by a slave’s name.
Slaves were often given a Christian first name and a surname
that identified their ethnicity (e.g., Tardieu [2001]). As well, a
slave’s ethnicity could often be determined from ethnic markings,
such as cuts, scars, hairstyles, or the filing of teeth (Karasch 1987,
pp. 4–9). Oldendorp (1777, p. 169) writes that “the people of all
Negro nations are marked with certain cuts on the skin. As far
as I have been able to learn from the Neg …
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