The institution of slavery extends back beyond recorded history. References to it appear in the ancient Babylonian code of Hammurabi. Its form and nature varied greatly in ancient society. It seems to have been common in the Tigris-Euphrates civilizations and in ancient Persia. In ancient Egypt slave labor was used in building temples and pyramids. The institution was familiar to the ancient Hebrews, according to passages in the Bible.

Slavery was an established institution in the Greece of Homer's time, and a large portion of the population of the Greek city-states in later days were of the servile class. There were domestic slaves, agricultural slaves, and artisans and workers. In Greece, although not quite as commonly as in Asia Minor, there were also public slaves, for example, those belonging to the temples. In general it is thought that slaves in the Greek city-states were relatively well treated, and there were laws protecting them against excessive cruelty or abuse. However, the slaves were regarded as property and had no rights in courts of law. Slaves could obtain their freedom by buying it, by being granted it in the owner's will, or as a reward for outstanding service.

Slavery in early Roman history seems to have been of the same type as in Greece, but by the 1st cent. B.C., as the Roman Empire continued to expand, a form of agricultural slavery called estate slavery was introduced on a wide scale; in this form agriculture was pursued by large numbers of slaves in an impersonal relationship with the landowner, who had practically absolute power over them. The increasing wealth of Rome led to an expansion in domestic slaves, and the servile class grew to great numbers. They were employed in the theater, in gladiatorial combats, and, to some extent, in prostitution. Most of the slaves were foreign, and some were highly educated and were employed as instructors. Having a large retinue of slaves became one of the prime marks of luxury, and exotic, especially Asian, slaves were in great demand. As the number of conquered provinces grew, so did the slave supply. Consequently, manumission (emancipation from slavery) was common, and freedmen became a significant factor in the Roman social system. The slave had almost no legal status, although custom mitigated against extreme brutality; the slave could testify against his or her master only in a very limited number of serious crimes (adultery, incest, and, later, lese majesty). As the Roman expansion abated, conditions of slavery improved somewhat.

The introduction of Christianity toward the end of the Roman Empire had no effect on the abolition of slavery, since the church at that time did not oppose the institution. However, a change in economic life set in and resulted in the gradual disappearance of the agricultural slaves, who became, for all practical purposes, one with the coloni (tenant farmers who were technically free but were in fact bound to the land by debts). This process helped prepare the way for an economy in which the agricultural slave became the serf.

The semifreedom of serfdom was the dominant theme in the Middle Ages, although domestic slavery (and, to some extent, other forms) did not disappear. The church began to encourage manumission, while ignoring the fact that many slaves were attached to church officials and church property. Sale into slavery continued to be an extreme punishment for serious crimes.

Slavery flourished in the Byzantine Empire, and the pirates of the Mediterranean continued their custom of enslaving the victims of their raids. Islam, like Christianity, accepted slavery, and it became a standard institution in Muslim lands, where most slaves were African in origin. In Islamic life, keeping slaves was largely a sign of wealth, with slaves used as soldiers, concubines, cooks, and entertainers and to perform a variety of other functions. Another form of Muslim slavery was in the eunuch guardians of the harems; eunuchs had been widely known in Greek, Roman, and especially Byzantine times, but it was among the Muslims and in East Asia that they were to survive longest. In Muslim countries, slavery and freedom had a much more fluid boundary than in the West, with some slaves and former slaves reaching positions of great power and prestige.

In Western Europe slavery largely disappeared by the later Middle Ages, although it still remained in such manifestations as the use of slaves on galleys. In Russia slavery persisted longer than in Western Europe, and indeed the serfs were pushed into the classification of slavery by Peter the Great.

A revolution in the institution of slavery came in the 15th and 16th cent. The explorations of the African coast by Portuguese navigators resulted in the exploitation of the African as a slave, and for nearly five centuries the predations of slave raiders along the coasts of Africa were to be a lucrative and important business conducted with appalling brutality. The British, Dutch, French, Spanish, and Portuguese all engaged in the African slave trade. Although Africans were, as early as 1440, brought back to Portugal, and although subsequent importations were large enough to change distinctly the ethnography of that country, it was not in Europe that African slavery was to be most profitable and widespread, but in the Americas, where European exploitation began at the end of the 15th cent.

The first people to be enslaved by the Spanish and Portuguese in the West Indies and Latin America were the Native Americans, but, because the majority of Native American slaves either revolted or escaped, other forms of forced labor, akin to serfdom, were introduced (see repartimiento and encomienda). The resistance of the Native Americans to slavery only increased the demand for Africans to replace them. Africans proved to be profitable laborers in the Caribbean islands and the lowlands of the South American mainland. In the colder highlands Native American slavery or quasi-slavery continued; long after the introduction of the first Africans the Paulistas (inhabitants of the city and state of São Paulo, Brazil) continued their slave raids against the Native Americans of the Brazilian hinterlands. But African slavery gradually became dominant.

The first Africans arrived in the British settlements on the Atlantic coast when they were traded or sold for supplies by a Dutch ship at Jamestown, Va., in 1619. They may have been indentured servants, but by the 1640s lifetime servitude existed in Virginia, and slavery was acknowledged in the laws of Massachusetts. The raising of staple crops—coffee, tobacco, sugar, rice, and, much later, cotton—and the rise of the plantation economy made the importation of slaves from Africa particularly valuable in the Southern colonies of North America. The slave trade moved in a triangle; setting out from British ports, ships would transport various goods to the western coast of Africa, where they would be exchanged for slaves. The slaves were then brought to the West Indies or to the colonies of North or South America, where they were traded for agricultural staples for the return voyage back to England. Later, New England ports were included in this last leg. The number of slaves in the colonies increased until in some (notably French Saint-Domingue, the modern Haiti) they constituted a majority of the population. In America by the date of the Declaration of Independence (1776) about one fifth of the population was enslaved.

British humanitarians who had incorporated the abolition of slavery into their conception of Christianity labored successfully to outlaw (1807) the British slave trade. These same men, especially William Wilberforce, Thomas Clarkson, Zachary Macaulay, and Lord Brougham (Henry Peter Brougham), continued to work for the abolition of slavery throughout the British Empire, which was finally effected with the Abolition Act of 1833. However, according to some writers, the British, in abolishing slavery, were primarily motivated by economic, not humanitarian, interests. These critics argued that, while the institution produced great wealth under the mercantilist system, it became unprofitable with the rise of industrial capitalism, which displaced mercantilism early in the 19th cent. At any rate, the abolition legislation of 1833 was followed by the gradual abolition of slavery in all lands under British control, principally by the device of invalidating the legality of slavery and removing its legal safeguards, usually by recompensing the owners.

Slavery proved unprofitable in the Northern states and by the early 19th cent. had disappeared. Its abolition had been hastened by the work of the Quakers, who, as in Great Britain, were staunchly opposed to the institution. In the South, however, where African slaves arrived in the tens of thousands from the late 17th through the early 18th cent., slavery came to be an integral part of the plantation system (especially after the introduction of the cotton gin in 1793). From the late 18th cent. to the eve of the Civil War, more than a million slaves were moved from the Eastern Seaboard to the Deep South, where many labored in the sugar and cotton fields. This vast internal slave trade, which often tore slave families apart, was the South's second largest enterprise; only the plantation system itself surpassed it in size.

In the Northern United States, humanitarian principles led to the appearance of the abolitionists. They knew little of the actual conditions in the South and were fighting not for economic reform but for idealistic principles. The abolitionists in general tended to regard slavery as an unmitigated evil. The small Northern farmer also feared slavery as a system of cheap labor against which it was difficult to compete.

The South, eager to conserve the status quo, developed a bellicose defense of the system, which was hardened by such factors as the slave uprising led by Nat Turner, the troubles over fugitive slaves, and the very active propaganda against the South. The question, involving the very existence of Southern society as then organized, was the dominant one in U.S. history from 1830 to 1860. The political expression of the struggle was largely an attempt on the part of the South to maintain legislative guarantees of the system against the efforts of the abolitionists.

The chief question concerned the right of extension of slavery in the Western territories. This first became important in 1820 with the Missouri Compromise. Many leading statesmen of the time sought an answer: Henry Clay, the great compromiser; Daniel Webster; John C. Calhoun; Stephen A. Douglas, who proposed popular sovereignty as means to decide the free or slave status of territories; and the uncompromising antislavery men, such as Charles Sumner and William H. Seward. The great compromises—the Missouri Compromise, the Compromise of 1850, and the Kansas-Nebraska Act—were ultimately ineffective.

Sectional opposition, which involved even broader questions than slavery, including the constitutional issue of states' rights, grew more passionate as the two sections became more and more hostile. The Ostend Manifesto and the proposed annexation of Cuba, the fugitive slave laws, the operations of the Underground Railroad, the furor caused by the Dred Scott Case, the Wilmot Proviso—all heightened the tension. Sporadic armed conflict erupted in Kansas and in the Harpers Ferry raid of John Brown. The struggle became more clearly defined as the Republican party was formed with a definite antislavery platform.

In the victory of the Republican presidential candidate, Abraham Lincoln (1860), the South saw a threat to Southern institutions, and the Southern states in an effort to secure those institutions resorted to secession and formed the Confederacy. The Civil War followed, and the victory of the North brought an end to slavery in the United States. Lincoln's Emancipation Proclamation (issued in 1863, it declared all slaves in the Southern secessionist states free) was followed by other legislation, especially the Thirteenth Amendment to the Constitution.

The end of the Civil War did not result in the integration of the former slaves into American life. Although there were gains toward this under Reconstruction, these were subsequently reversed by the Jim Crow laws. Generally easily identified by the color of their skin, African Americans were subjected to segregation and other forms of discrimination practiced by most white Americans and legislated in many jurisdictions. This situation did not begin to be ameliorated until the civil-rights struggles of the 20th cent. (see civil rights; integration).

In the late 20th cent. the idea of compensating American blacks for their enslavement through some form of reparations won widespread support from African-American organizations and greater notice, although little support, from the broader society. The reparations movement was spurred in part by payments to Holocaust victims, to Japanese Americans interned during World War II, and to some Native American tribes. Unlike these groups, however, reparations for slavery would be paid to individuals who are descendants by several generations of the victims, instead of to the victims or to a tribal people. Supporters of reparations, however, argue that contemporary African Americans continue to suffer from the vestiges of slavery and the discrimination that followed emancipation.

In other countries emancipation of slaves was also a serious problem, but never to such an extent as in the United States, chiefly perhaps because the question of race prejudice was nowhere else so important. As the South American nations gained independence, they broadened their democratic principles to include absolute prohibition of slavery (Chile in 1823, Central America in 1824, Mexico in 1829, and Bolivia in 1831) or gradual emanicpation (Argentina in 1813, Colombia in 1814, and Venezuela in 1821). In Brazil the opposition of the planters to abolishing slavery was strong, and it was only after a series of rather ineffective measures that the slaves were emancipated in 1888. Opposition to that action helped to launch the revolution of 1889.

In later years the slave trade was conducted on the east coast of Africa, the market being in Muslim lands. Most antislavery efforts during the 19th cent. were directed against slave trading. Great Britain had passed antislave-trade laws in 1807 and 1811; the British attempted to enlist other nations in an effort to stop the slave trade, and several treaties for such a purpose were signed in the 1840s. However, the first important international agreement was not reached until the Berlin Conference in 1885, which bound the more important Muslim potentates to act against the slave traffic. This was supplemented by the even more significant Brussels Act of 1890, to which 18 states were signatory.

The emperor of Abyssinia (Ethiopia) was unable to prevent traffic from that land to Arabia, and a brisk trade went on over the Red Sea. International scandals occurred from time to time with regard to forced labor; three notable ones concerned the Congo, Liberia, and the Putumayo region of Peru in the 1930s (Native American servitude). The League of Nations adopted the resolutions of the International Slavery Convention of 1926, which was considered an advance over the Brussels Act of 1890; its main weakness was in not providing a permanent commission to oversee the total abolition of slavery. Slavery continued to exist in parts of Asia, the Middle East, and, despite increasingly successful efforts to abolish it, in various parts of Africa.

The United Nations has continued the efforts of the League of Nations to achieve worldwide abolition of slavery. The Declaration of Human Rights, adopted by the General Assembly in 1948, contained a provision prohibiting slavery or trading in slaves. The Security Council in 1954 condemned systems of forced labor, particularly those employed as a means of political coercion. In 1956 a UN conference of plenipotentiaries adopted a convention on the abolition of slavery; an important aspect of the convention was the inclusion of other institutions similar to slavery as practices to be abolished. However, a report prepared for the United Nations in 1966 charged that slavery still existed in parts of Africa and Asia. Although efforts to end involuntary servitude continued throughout the last half of the 20th cent., by the beginning of the 21st cent. forms of slavery, forced, or bonded labor still persisted in a number of Third World countries, e.g., Sudan, Mauritania, Niger, Myanmar, Pakistan, and the Amazon region of Brazil. More isolated instances have been occasionally revealed elsewhere, e.g., involving Asian immigrants in the United States.