The legal trans-Atlantic slave trade reached unprecedented levels in the late eighteenth century, but by the mid-nineteenth century every national carrier in Europe and the Americas had formally abolished the traffic. Denmark was the first nation to abolish its trade in 1803. Britain and the United States followed in 1807, with the U.S. ban going into effect in 1808. By 1836, the Dutch, French, Spanish, Brazilian, and Portuguese governments had also abolished their trades. During just three decades, every national trans-Atlantic carrier outlawed a massive system of forced migration that had lasted for three centuries.
According to historians, the relatively rapid abolition of the trans-Atlantic slave trade is explained by ideological, religious, and economic change in Europe and the Americas. There is much debate about which factor was most important. Scholars of the ideological school identify abolitionism’s origin in the Enlightenment. This influential eighteenth century intellectual movement suggested that all men (and to an extent women) held certain rights. Among these rights was liberty, which the slave trade clearly violated. Other scholars privilege the role of some evangelical religious groups, such as the Quakers, who by the late eighteenth and early nineteenth centuries saw abolitionism as an expression of “Christian love” for their fellow man. Other historians emphasize economic motives. One early theory was that Britain abolished its slave trade because British Caribbean plantations were becoming less profitable and needed fewer new slaves. Today most scholars contest this theory, and argue that slavery and the slave trade were still profitable when the trades were banned in the nineteenth century.
The case of U.S. abolitionism indicates that this blend of ideological, religious, and economic factors varied according to specific national contexts. In Early America, black and white abolitionists channeled the spirit of both the Enlightenment and the American Revolution in their cries for "liberty." In addition, American anti-slavery evangelicals spread their message widely in the United States. On the economic front, slavery and the slave trade had become increasingly marginal to the livelihoods of many northerners, which weakened their resistance to the abolition of the slave trade. At the same time, in the Upper South, politically influential slaveholders supported abolition in order to strengthen the domestic slave trade to Lower South. These planters believed that if the trans-Atlantic trade was not abolished, it would compete with the domestic traffic in supplying slaves to the Lower South, where plantations were expected to flourish in the nineteenth century.
The trans-Atlantic slave trade was an international industry, which meant that international cooperation was required to enforce abolition once national bans were in place. In the early nineteenth century, many governments representing former slaving powers signed multi-national anti-slave trade treaties. These accords affirmed signatories’ commitments to abolition, established common standards for banning slave-trading equipment from commercial vessels, and outlined joint commitments to maintain anti-slave trade patrols in African and Caribbean waters. Britain provided the largest and most effective anti-slave trade fleet, but France, Portugal, and the United States also manned lightly-armed flotillas. In addition, most powers recognized a newly established network of international courts designed to adjudicate illegal slave trading cases, known as the Courts of Mixed Commission. By the mid-nineteenth century, these courts were established in Brazil, the Caribbean, West Africa, and South Africa.
Despite these efforts, abolition legislation and international cooperation did not end the trans-Atlantic slave trade. Although abolition was largely implemented in the British and French empires, and only a few slave ships are known to have arrived on U.S. shores after 1808, slave importations to Brazil, Cuba, and Puerto Rico actually increased after the trade was outlawed. Underdeveloped plantation economies in these jurisdictions created huge demand for slave labor and record profits for illegal slave traders. Most Brazilian and Cuban policymakers linked economic growth with continued slave imports, and many tacitly supported the illegal traffic.
Similarly, in Africa, polities with long slave-trading histories such as Dahomey and Ngoyo were unwilling or unable to halt the supply of captives to the coast, or to expel foreign slave dealers who resided there, despite commitments to do both. Meanwhile, the illegal slave trade became increasingly difficult to suppress. British and American merchants engaged indirectly in the traffic by supplying Latin American slave traders with ships and goods exchangeable for captives on the African coast. The U.S. government also denied other nations the right to search U.S. ships suspected of slave trading, and soon a large portion of the entire illegal trans-Atlantic slave traffic took place under the shield of the U.S. flag. Under these conditions, slave imports to Brazil and Cuba rose to levels higher than those before abolition.
Suppression of the illegal trans-Atlantic slave trade only became effective when external pressures on slave-importing regions were bolstered by changing public opinions within those societies. In 1850, domestic reformers in Brazil forced a clampdown on the illegal slave trade with the assistance of a British naval blockade of Rio de Janeiro. At that point, Cuba became the last large-scale slave importation zone. It was not until 1867, after widespread abolitionist pressure within the Spanish empire—and in light of emancipation in Cuba’s much larger neighbor, the United States, after a violent civil war—that the Spanish government moved decisively against the illegal trans-Atlantic slave trade, ending the traffic for good.