Christian and Muslim Roles in the Atlantic and Indian Ocean Slave Trades

Origins and Systems of Enslavement

When most people think of the slave trade, the image that comes to mind is the transatlantic system: ships crammed with human beings, sailing from West Africa to the Americas, feeding the rise of plantation economies. This trade was indeed vast and devastating, carrying over twelve million Africans across the ocean between the sixteenth and nineteenth centuries.

But it was not the only global slave system. Long before the Atlantic trade began, and overlapping with it for centuries, there was also the Indian Ocean slave trade — a vast network moving Africans eastward into Arabia, Persia, India, and the islands of the Indian Ocean. To understand slavery as a global phenomenon, we must examine both systems together. When we do, a sobering truth emerges: both Christian and Muslim societies, despite sacred teachings on compassion and human dignity, actively participated in, justified, and profited from slavery.

Both systems reveal the same moral paradox — that theology, when bound to empire, sanctifies exploitation.

Two Worlds, One Logic

The Atlantic and Indian Ocean trades differed in scale and structure but shared an underlying logic.

The Atlantic trade, built on European expansion, was state-sponsored, race-based, and tied to the rise of plantation capitalism in the Americas.
The Indian Ocean trade, older and more diffuse, wove slavery into long-established commercial and cultural networks stretching from East Africa to South Asia.

While the Atlantic system turned race into property, the Indian Ocean network turned difference into dependency — both made hierarchy holy.

Early Christian Involvement in Africa

By the mid-1400s, Christian Europe was entering the Atlantic world. Portuguese explorers sailing down Africa’s west coast sought to bypass Muslim intermediaries and reach the fabled gold of West Africa. But soon they discovered another commodity: people.

In the 1440s, Portuguese ships began seizing captives in what is today Senegal and Mauritania. Some were taken back to Portugal, where they were sold in markets and forced into household labor. Others were shipped to the newly colonized islands of Madeira, the Azores, and São Tomé, where sugar plantations were being established. These plantations became laboratories for the mass-enslavement system later exported to the Americas.^1

The Church’s Sanction

The Catholic Church offered theological cover for these ventures. In 1452, Pope Nicholas V issued the papal bull Dum Diversas, granting Portugal the right “to invade, search out, capture, and subjugate all Saracens, pagans, and other unbelievers … and to reduce their persons to perpetual servitude.”^2 This was no fringe opinion but an official decree from the highest religious authority in Europe.

In 1493, Pope Alexander VI issued bulls (notably Inter caetera) drawing an initial line of demarcation; Spain and Portugal then negotiated the Treaty of Tordesillas (1494), which moved that line westward and divided spheres of conquest between the two crowns.^3 The papacy thus transformed mission into mandate and conquest into Christian duty.

From the outset, the Atlantic slave trade was wrapped in the mantle of divine legitimacy — even as it contradicted the Christian claim that all humans are made in the image of God.

Early Muslim Involvement in Africa

While Iberian ships turned westward across the Atlantic, Muslim traders had long turned eastward across the Indian Ocean. As early as the seventh and eighth centuries, after the spread of Islam, merchants sailing dhows along the East African coast began purchasing or capturing Africans for export.

These captives were sent north to Arabia and Egypt, east to Persia and India, and across the Indian Ocean to the Comoros, Madagascar, and parts of Southeast Asia (including Java).^4 Unlike the Atlantic trade, which developed rapidly in the fifteenth century, the Indian Ocean trade was older and woven into pre-existing networks of commerce and pilgrimage.

Law and Practice

Islamic law (sharia) did not forbid slavery outright but sought to regulate it. Enslavement was allowed only under specific conditions — usually capture in warfare or birth to enslaved parents. Slaves were to be treated humanely, and manumission was considered a pious act. The Prophet Muhammad is reported to have said:

“Your slaves are your brothers; feed them from what you eat and clothe them as you clothe yourselves.” (Ṣaḥīḥ Muslim, 1661)^5

Yet practice often diverged from principle. Slave markets thrived in Cairo, Baghdad, Zanzibar, and Muscat. Women were in high demand as domestic servants and concubines; children were taken for household labor. Men were conscripted as soldiers, pearl divers (a documented role for enslaved Africans in the Gulf), sailors, and agricultural workers. The Zanj Rebellion of 869–883 CE — when African slaves rose up in southern Iraq — stands as a stark testament to the brutality and scope of this system.^6

The dissonance between scripture and practice reveals how economic systems reshape moral reasoning. The Qur’an’s encouragement of kindness and liberation became, in the hands of rulers and merchants, a justification for the very opposite.

Economic Drivers and Religious Justifications

Why did both Christian and Muslim societies embrace slavery despite their faiths’ ethical teachings? The answer lies in economics and power.

In Christian Europe

The “discovery” of the Americas created a desperate need for labor. Native populations, devastated by disease and warfare, could not sustain plantation economies. Africa provided the answer. European merchants — backed by Christian monarchs and theological decrees — constructed the triangular trade that enriched empires and fueled early capitalism.^7

Church doctrines and royal charters worked hand in hand: the Casa da Guiné and later the Casa da Índia managed Portugal’s African trade under religious license, enforcing crown monopolies that included slave traffic through Mina and Lisbon. Conquest became an act of faith and profit simultaneously.

In the Islamic World

Demand came from multiple directions — for domestic service, military labor, concubinage, and plantation work. The Swahili city-states of Kilwa and Mombasa, and later Zanzibar under Omani rule, became regional hubs. Local African elites, both Muslim and non-Muslim, collaborated with Arab and Persian traders to capture people from the interior and march them to the coast.

Profits flowed both ways: inland chiefs gained firearms and luxury goods; coastal traders grew rich on human commerce.^8 In this moral economy, enslavement was rationalized as lawful exchange — a tragic fusion of faith and finance.

Moral Parallels Across Oceans

Despite doctrinal differences, both Christian and Muslim worlds bent toward the same gravitational pull: profit sanctified by scripture. Papal bulls and royal charters in Europe, fatwas and commercial law in the Islamic world — each provided spiritual scaffolding for systems of bondage.

It was not Christianity rooted in the Sermon on the Mount, nor Islam rooted in the Prophet’s compassion, but something else entirely: religion as empire, and empire as theology.

In both worlds, theology provided not a brake on exploitation, but a vocabulary for it. The wilderness, whether Atlantic or Indian, became sacred through conquest.

Conclusion: Faith and Enslavement Entwined

By the fifteenth century, both Christian and Muslim empires had embedded slavery within their moral and commercial worlds. Their scriptures had been reinterpreted to bless domination; their economies had come to depend on human bondage.

For now, the lesson is clear: the two faiths that proclaimed the unity of humanity both helped divide it — proving that no religion is immune from the corruptions of power, and no empire innocent in the making of slavery.

Endnotes

John K. Thornton, Africa and Africans in the Making of the Atlantic World, 1400–1800, 2nd ed. (Cambridge: Cambridge University Press, 1998), 36–40.
Dum Diversas, papal bull of Nicholas V (1452), in European Treaties Bearing on the History of the United States and Its Dependencies to 1648, ed. Frances Gardiner Davenport (Washington, DC: Carnegie Institution, 1917), 23–25.
Basil Davidson, The African Slave Trade: Precolonial History, 1450–1850 (Boston: Little, Brown, 1994), 34–36.
Paul E. Lovejoy, Transformations in Slavery: A History of Slavery in Africa, 3rd ed. (Cambridge: Cambridge University Press, 2012), 29–32.
Ṣaḥīḥ Muslim 1661 (The Translation of the Meanings of Ṣaḥīḥ Muslim, Riyadh: Darussalam, 2007).
Patricia Crone, Slaves on Horses: The Evolution of the Islamic Polity (Cambridge: Cambridge University Press, 1980), 80–82.
Philip D. Curtin, The Atlantic Slave Trade: A Census (Madison: University of Wisconsin Press, 1969), 95–101.
Frederick Cooper, Plantation Slavery on the East Coast of Africa (New Haven: Yale University Press, 1977), 21–24.

Bibliography

Allen, Richard. Slavery and Freedom in Indian Ocean Africa and Asia. Athens: Ohio University Press, 2010.
Cooper, Frederick. Plantation Slavery on the East Coast of Africa. New Haven: Yale University Press, 1977.
Crone, Patricia. Slaves on Horses: The Evolution of the Islamic Polity. Cambridge: Cambridge University Press, 1980.
Curtin, Philip D. The Atlantic Slave Trade: A Census. Madison: University of Wisconsin Press, 1969.
Davidson, Basil. The African Slave Trade: Precolonial History, 1450–1850. Boston: Little, Brown, 1994.
Davenport, Frances Gardiner, ed. European Treaties Bearing on the History of the United States and Its Dependencies to 1648. Washington, DC: Carnegie Institution, 1917.
Lovejoy, Paul E. Transformations in Slavery: A History of Slavery in Africa. 3rd ed. Cambridge: Cambridge University Press, 2012.
Thornton, John K. Africa and Africans in the Making of the Atlantic World, 1400–1800. 2nd ed. Cambridge: Cambridge University Press, 1998.