The abolition (ending) of slavery over the course of the nineteenth century and into the beginning of the twentieth marked an important moment in world history, especially in the Atlantic. In 1800, plantations worked by enslaved people, particularly Africans, stretched across the Americas. These plantations were sustained by a murderous system that brought tens of thousands of captives every year from Africa to the Americas in the most horrendous conditions. Their initial capture and enslavement and journey across the Atlantic posed so many dangers that many died before leaving the boat. Those who survived suffered a life of harsh labor, atrocious (terrible) living conditions, and an almost complete lack of rights or security until their deaths. Slavery existed elsewhere in the world— particularly in South Asia and the Islamic World—but nowhere was it as extensive or deep-rooted as in the Americas.

Then, beginning in 1803, slavery and the slave trade were outlawed in many parts of the world, beginning with the European and American countries that benefited most from these institutions. In 1803, Denmark made it illegal for its citizens to participate in the Atlantic slave trade. In 1807-1808, both the United States and Britain criminalized the importation of slaves into their territory. (But they continued to enslave the people they had already imported, as well as their descendants.) Independent Haiti became the first country in the Americas to abolish slavery in 1804, followed by Cuba in 1886, Mexico in 1829, and much of Latin America soon after. The United States would not follow suit until after the Civil War in 1865. Meanwhile, the major European slave-trading powers gradually abolished the trade—the Netherlands in 1814, followed by Portugal, Spain and France by 1820. Of course, enslaved people were still smuggled into the Americas, in particular to Cuba and Brazil, where it remained legal until quite late in the nineteenth century. But the tide had definitely turned, and slavery would be outlawed in many other regions of the world in the years that followed.

Why did abolition just “happen” in the nineteenth century? What shifted in this era that caused some of the biggest slave-owning and slave-trading societies to suddenly become abolitionists? There are at least three important theories to consider.

Theory 1: Free labor and free wages

Perhaps the most dramatic shift toward abolitionism at the end of the eighteenth century occurred in Britain and parts of English-speaking North America. In the 1790s, Britain had the world’s largest slave trading industry. One of Britain’s largest companies, Lloyd’s of London, insured almost every slave trading voyage between Africa and the Americas. In 1807, however, Britain became the first large country to criminalize the slave trade. In 1835, slavery was abolished throughout the British Empire. English-speaking northern U.S. states and parts of Canada followed quickly. In 1827, for example, New York passed a law abolishing slavery in that state. What changed in these regions?

One theory is that it was economic. Some argued that the emerging middle class, especially in Britain, believed that slavery didn’t really help them economically. These middle-class industrialists and business owners did their work without slaves. Their only participation was that they had occasionally invested in slave trading voyages, but profits were dropping in that terrible industry. Instead, they invested in businesses that paid wages to its workers. As a result, they saw slavery as unfairly competing with these businesses. Also, the slave trade created chaos in Africa. Many of these business people were hoping to make money from trade in Africa by selling finished goods to Africans and buying palm oil and other African resources to use in their factories. Ending the slave trade, they hoped, could make business in Africa more stable and profitable.

Of course, this class of businesspeople generally believed in the Enlightenment ideal of freedom. These ideals included “free labor”—people paid wages for their work rather than enslaved. So their support for abolition was partly philosophical. But it is important that they also hoped to benefit financially from abolition. Additionally, these businesspeople were often competing for power politically with an older upper class of land-owning nobles, many of whom made their money partly from slave plantations. Ending the system of slavery could undercut their political opponents and help level the playing field.

Thus, as historian (and later prime minister of Trinidad and Tobago) Eric Williams argues, it can be argued that slavery was only abolished when it made economic sense for some people.

Theory 2: Morality

Not everyone agrees that money and economic motives were at the heart of abolitionism. Philosopher John Stuart Mill, who lived in this period, argued that abolition was a result not of “’any change in the distribution of material interests,” but rather “by the spread of moral convictions.” Mill wrote: “It is what men think that determines how they act.”

These changing ideas may have had something to do with the Enlightenment. In the late eighteenth century, a new conversation about morality was emerged in Europe. Thinkers were debating who was human, and developing ideas about the brotherhood of men. These discussions inspired many leaders of the French Revolution and got people talking about the morality of slavery. The most famous image of the abolitionist movement is of a black man in chains, asking “Am I not a Man and Brother?” But there were limits to this brotherhood. In general, the new morality did not see enslaved blacks as equals.  Even in this famous image, the enslaved man is depicted looking up to the European viewer, powerless and on his knee. These Enlightenment ideas were partly a result of new ways to interpret the Bible. Slavery had often been defended through readings of Old Testament texts that seemed to justify enslavement, especially of Africans. Some abolitionists were humanists (those who believed strongly in the worth of individual humans) who rejected these texts entirely. But most of the leaders of the movement—especially in Britain—were actually evangelical Christians who found new freedoms to reread these texts. Noting that the gospel called for “goodwill towards all men,” they argued that slavery went against the spirit of Christianity.

We can’t forget that many of these same evangelical abolitionists were also businessmen who stood to profit from the abolition of slavery. However, at the same time working-class people in Britain and other locations began in the 1790s to support the abolition of the slave trade, even though they knew it wouldn’t really affect the working class financially. They were motivated by a belief that the slave trade was evil, and that supporting abolition was the moral and ethical thing to do. Their main weapon was a boycott of sugar and rum, two products produced overwhelmingly by slaves. This was pretty hard for many workers, but—often led by their wives, who did the buying—working class families around Britain stopped using sugar in 1792 in support of a ban on the Atlantic slave trade. They did it again in the 1820s during the campaign to abolish slavery across the empire. These families had little reason to boycott two of their favorite products, except for the moral issues. For some it was probably true morality, for others it may have been a more self-serving wish to make others see them as moral.

Theory 3: The actions of Africans in the Americas and Europe

There is another theory about abolition that does not focus on the actions of white Europeans. This theory argues black Americans and Europeans—many of them formerly enslaved or the descendants of slaves—took actions that led to the end of slavery.

This story centers partly in Britain, where some of the most effective abolitionists in the 1790s were black. One of these leaders was Olaudah Equiano, a formerly-enslaved man who liberated himself and lived in Britain. Equiano was baptized a Christian after his capture. In his autobiography, he used the Bible to show how the disciple Paul had clearly stated that slavery conflicted with Christian belief. His book was one of the most powerful abolitionist texts of the day, and he spoke against slavery all across Britain. Another free African, Ottobah Cugoano, also played an important role and called for the abolition of slavery in his autobiography.

Black abolitionists played an even more significant role in France and its empire. During the French Revolution, black Frenchmen and Frenchwomen called for an end to slavery. They included Jeanne Odo, a woman who was born in the vast plantation colony of Saint-Domingue, as well as Jean-Baptiste Belley, a Senegalese man who had been sold into slavery in Saint-Domingue (now called Haiti). Odo, Belley, and others tried to get the French constitution to outlaw slavery. But undoubtedly the biggest leap toward ending slavery was the Haitian Revolution. A dramatic uprising of enslaved people suddenly stopped slavery in what had been the largest plantation colony in the French Empire. It was only by overthrowing the whole system, and fighting off the French army, that the enslaved population gained its freedom. Next, by removing France’s largest slave colony from the empire entirely, they created conditions for empire-wide change. Although France allowed slavery to continue in its remaining colonies in the 1820s and 1830s, by 1848 it would be abolished across the French Empire. As historian Sylviane Diouf notes, “It is now recognized that without the impulsion [force] of the revolt in Saint-Domingue, the French Revolution would not have decreed [ordered] the abolition. The Haitian Revolution had radicalized the French Revolution on the question of slavery.”

In Mexico in the 1820s abolitionism was also led by people of African descent. Abolition was eventually declared for almost all of Mexico in 1829, by Vicente Guerrero, a president of partly African ancestry. The United States, however, wouldn’t abolish slavery nationally for another three and a half decades.

Conclusion

Gradually, most of the world’s nation-states abolished slavery by the beginning of the twentieth century—barely over 100 years ago. There was a belief that capitalism would eventually drive out all aspects of slavery in favor of wage labor done by free workers. In reality, however, forms of slavery remained (and still remain today). In some places, slavery went underground but continued to exist, as in many parts of the Islamic World. In other places, like South Asia, class systems and other types of restrictions meant that many people were kept in terrible conditions and subjected to harsh work with no real escape. In the United States and many parts of the Americas, racial systems continued to restrict and oppress many of the formerly enslaved, while sharecropping and other economic systems amounted to slave labor.