With the rise of European economic and military dominance between the 15th and 18th centuries, the character of slavery changed. During the medieval era (ca. 500–1500), the number of slaves sold out of Africa had remained stable at a few thousand a year, with most being carried by caravan to the Middle East. By the 17th century, the number of slaves from Africa had jumped to tens of thousands annually, with most being carried on ships across the Atlantic Ocean to the Americas (see African forced migration). During the 18th century, the Atlantic slave trade peaked, in some years reaching more than 100,000. Also, for the first time, slavery became closely associated with race. Historically, in most slave-holding societies, slaves and slave owners were of the same race. In the 15th and 16th centuries, Spain and Portugal extended their rule over American, African, and Asian territories populated by different races of people. With rich mines and tropical territories well suited to the cultivation of labor-intensive cash crops such as sugarcane, cotton, and coffee, Iberian Europeans naturally looked for labor locally. Native Americans were at first enslaved, though later officially protected by being brought under a feudal system of forced labor and taxation (encomienda) that left them with few personal freedoms. As settled native peoples were exterminated by hard labor and disease, Spain and Portugal increasingly turned to Africa, where the Portuguese had established a permanent presence along the east coast from the 1480s. In 1516, Spanish king Charles I (Holy Roman Emperor Charles V) granted an asiento to bring 4,000 African slaves annually into New Spain, a number that steadily increased so that by the end of the 19th century, more than 5 million slaves had been brought from Africa to Spanish and Portuguese New World colonies.
By the 17th century Holland, Britain, and France were challenging the colonial supremacy of Spain and Portugal and developing similar slave plantation economies throughout the Caribbean Basin. By the early 19th century, more than 3 million slaves were brought into British, French, and Dutch colonies in the New World. In the early days of British and French settlement in North America, most labor was performed by indentured servants (see indentured servitude), but with passage of the navigation acts, falling tobacco prices, and the difficulty of securing labor, the demand for new sources of labor grew. In 1662, the British government sought to meet the demand by granting a monopoly of the slave trade in its territories to the Royal African Company. In the same decade, slave codes based on old Roman models began to be enacted throughout the southern colonies, legally establishing the condition of slavery. The status of children followed that of mothers rather than fathers; slaves were increasingly forbidden to own firearms or other property, to travel freely, or to testify against white defendants; and the manumission of slaves was made more difficult. Thousands of Native Americans were enslaved, particularly in the wake of the devastating Carolina tribal wars between about 1680 and 1720. Given the Native American propensity for violence and escape, by 1715, New England colonies were already banning American Indian slavery, and continued warfare and disease soon ended attempts to systematically enslave them.
The legal and social conventions of slavery gradually developed into a doctrine of ethnocentric RACISM in which dark-skinned Africans—who were pagans and viewed as sexually licentious—were considered innately inferior to Europeans. The number of slaves in British North America grew dramatically in the 18th century. By 1770, slaves accounted for 40 percent of the population in Maryland, Virginia, and South Carolina. At the same time, slaves composed only about 5 percent of the population of the northern colonies and even less in Canada, where small farms predominated and economic conditions did not favor slavery. Altogether more than 600,000 Africans were brought as slaves to the United States. Through natural increase, by the mid-19th century their numbers had increased to almost 4 million.
The conditions under which slaves labored in North America varied greatly. Most worked as agricultural field hands, from sunrise to sunset and especially hard during the harvest. After harvest and before planting, animals had to be cared for and the numerous repairs of a farm or plantation attended to. Many also worked as domestic servants and in factories. A few became slave drivers, craftsmen, or skilled carpenters or blacksmiths. The attitude of slave owner toward slave varied as well. Many owners were brutal, inflicting severe beatings or mutilations for small infractions, sometimes forcing female slaves to engage in sexual acts. Others abjured violence except as a last resort and treated slaves almost as family members. Slave marriages were not legally recognized, but monogamy was encouraged. This did not stop slave holders from breaking up families when children reached young adulthood or when a high price might be commanded for a slave. The standard of living for most slaves was somewhat above the subsistence level, in large measure because they represented a valuable economic asset. Food tended to be adequate in quantity and generally healthy, though plain. Slave houses were drafty, without much furniture and usually without floors. In every case, however, slaves were at the mercy of their owners, who collectively created a social environment that made resistance virtually impossible. Slaves were not allowed to leave plantations without permission, education was prohibited, and manumission was discouraged. The relatively small number of slave revolts in the United States reflects the isolation of slaves and the complete lack of means for successful revolt. The most famous insurrection, the Nat Turner rebellion of 1831, involved a band of 75 slaves who killed more than 50 whites and unsuccessfully attempted to reach a local armory in Virginia. Within two days, the rebellion was quelled, and eventually all the rebels were killed or captured, and Turner himself was executed. For the most part, resistance to slavery was more subtle, involving deliberate slowing of work, the breaking of tools, and encouragement of the idea that slaves were naturally childlike and prone to laziness.
Until the middle of the 18th century, the morality of slavery had seldom been questioned anywhere in the world. With the enhanced emphasis on natural rights and political liberty that were characteristic of the Enlightenment and the humanitarian and religious activism associated with the Great Awakening, a strong antislavery movement developed in Britain, France, and America. These intellectual movements coincided with the beginnings of the industrial revolution, which shifted economic predominance from the land to the factory and other economic enterprises that did not benefit from slavery. The slave trade was abolished in Britain in 1807, in the United States in 1808, and in France in 1819. Slavery itself was banned throughout the British Empire, including the Canadian colonies, in 1833 when the government agreed to compensate slaveholders for their economic losses. In the United States, where slavery was more prevalent and had become more deeply entrenched with the rising importance of short-staple cotton from the 1790s, the abolitionist reform movement became more radical and found a commanding voice in William Lloyd Garrison, who founded the Liberator journal and encouraged free African Americans such as Frederick Douglass to speak at antislavery meetings. Garrison’s call for immediate and unconditional abolition of slavery polarized attitudes. Although most Americans were not convinced that slavery was morally wrong, many were troubled, and Garrison and other abolitionists did succeed in bringing the fate of nearly 4 million Americans of African descent to the national stage. The United States split into two political camps over slavery and eventually fought the Civil War to determine whether individual states or the federal government had the authority to regulate slavery. In 1863, President Abraham Lincoln freed all slaves under Confederate (southern) control, and in 1865, slavery was abolished with the ratification of the Thirteenth Amendment to the Constitution. African Americans were freed from slavery in 1865 but were systematically discriminated against until the Civil Rights movement of the 1950s and 1960s.