While the Code of Hammurabi, one of the most famous ancient law codes, propagated in Hammurabi's name in Babylonia sometime between 2100 and 1800 B.C., prohibited wanton cruelty in the treatment of slaves, it stipulated that slaves were to be branded on the forehead and forbidden to hide or mask the mark. (source)

Slavery appears to have been a universal institution in the ancient world. For example, it was never questioned in either the Old Testament or the New Testament. (source)

In ancient Egypt, slaves are known to have been murdered to accompany their deceased owners to the afterlife. (source)

Euripides.

The earliest person on the record as denouncing slavery as an evil was Euripides, who wrote in his play Hecuba, "That thing of evil, by its nature evil,/ Forcing submission from a man to what/ No man should yield to." (source)

In the year 1000, the world's largest slave market was run by Vikings in Dublin.

One of the many causes of the decline of the Roman Empire may have been their use of slave labour. While the ancient Greeks had many impressive scientific and mathematical achievements, they never succeeded in applying any of their discoveries to any practical use, in part because slave labour was cheap and readily available. By the end of the second century A.D., the ancient world's lack of industrial technology and labour-saving machines began to make it difficult for the Roman Empire to maintain both its military and a healthy civilian population.

St. Patrick (circa 385–461), who in his youth had been enslaved in Ireland, was the first prominent historical figure to speak out against slavery.

In ancient China, some slaveowners appointed their male slaves as their heirs if the slaveowners had no natural offspring. (source)

Slavery ended in Western Europe in the 7^th century, when a British girl, Bathilde, was enslaved and sold to King Clovis II of the Franks (638–655). Clovis fell in love with and married her. After the king died, Bathilde, acting as regent for their three young sons, outlawed slavery. She was later canonized as a saint by the Roman Catholic Church. (source)

Between 7 million and 10 million slaves were brought to the Americas from Africa. (source)

Russia can be seen as having been founded as a by-product of Viking slave raids in the ninth century. (source)

The word slave comes from Slav, the name of a group of Eastern European peoples. In antiquity, Germanic tribes captured Slavs and sold them as slaves to Romans. The Latin word for slave, addict, has become the English word for someone dependent on something harmful. (source)

While serving in Congress, Thomas Jefferson introduced a bill that would prohibit slavery in any state admitted to the United States in future. This measure, which could have prevented the American Civil War decades later, was defeated by a single vote. (source)

Slavery ended in the British Empire on August 1, 1834, when legislation passed in 1833 took effect. The legislation specified an apprenticeship scheme for the freed slaves that in some cases resulted in them being treated harsher than before, but slavery in any form in the Empire ended by August 1, 1838. The legislation also compensated slave-owners with £20,000,000; the slaves received nothing besides their freedom. (source)

In ancient Rome, many freed slaves, known as freedmen, were rich, and some achieved high positions in government. (source)

In Mesoamerica, where there were no draught animals, slaves were often used as porters. (source)

In Korea, before the middle of the 18^th century, between ⅓ and ½ of the population were slaves. (source)

In the year 1086, around 10% of the population of England listed in the Domesday Book were slaves; the percentage was as high as 20% in some areas. (source)

In 1850, the state of Michigan's constitution read, "Neither slavery nor involuntary servitude, unless for the punishment of crime, shall ever be tolerated in this state," inadvertently legalizing slavery as an appropriate punishment for crime. It was not until 1963 when the comma was shifted from its position after servitude to a position after slavery, outlawing slavery as punishment for crime. (source)

The worst law ever passed by the United States federal government may have been the Fugitive Slave Act of 1850. Fugitive slave legislation had been around since 1793, but the new act gave law enforcement officers in the Northern States carte blanche to pursue and arrest fugitive slaves, and even to compel civilians to assist. Slaves so captured would be sent back south, without being able to defend themselves or produce evidence that they were not in fact slaves. Furthermore, the arresting officer received a bounty of $10 for each slave returned. Despite the significant incentives to catching slaves, only about 300 slaves were captured and returned between 1850 and 1861. The only real effect that the Fugitive Slave Act had was to exacerbate bad feelings between the southern states and the northern states, which would lead to the U. S. Civil War in 1861. (source)

In 1853 Illinois passed a law requiring any black entering the state and staying more than ten days to pay a fine of $50. If he could not pay, he could be sold into slavery for a period commensurate with the fine. (source)

The Emancipation Proclamation freed very few slaves immediately. Issued by Abraham Lincoln on January 1, 1863, the proclamation applied only to slaves in areas controlled by the rebel Confederate government, where Lincoln had no authority to enforce it. (source)

In the American Civil War, Robert E. Lee, general-in-chief of the Confederate armies that fought to maintain slavery, was morally opposed to slavery; he had freed his slaves in the late 1840s, believing that "slavery as an institution is a moral and political evil in any society, a greater evil to the white man than the black". (source)

The country of Liberia was founded as a voluntary haven for freed American slaves. The American Colonization Society purchased the land from tribal chiefs in 1822; the price included, among other items, a box of beads, three pairs of shoes, a box of soap, a barrel of rum, and 12 spoons. (source)

In the early 16^th century, Native Americans were enslaved by the Spanish in the New World. In 1517, missionary Bartolomé de Las Casas, sickened by this practice, was the first to suggest enslaving Africans instead. He would end up regretting this suggestion. (source)

In the late eighteenth century, slavery was dying out in not only the northern but also the southern United States. The man indirectly responsible for its perpetuation was Eli Whitney, whose cotton gin, invented in 1793, was so efficient that it injected new life into the stagnant southern economy, dooming blacks to another 70 years of slavery. (source)

Patrick Henry, an American political leader famous for saying "Give me liberty, or give me death", owned 65 slaves when he died in 1799. (source)

In the Thai language, one shows politeness by using the word "slave" for "I". (source)

Slaves have almost always been used where they would be cheaper and more productive than hired workers. Therefore, in societies that used many slaves, including ancient Rome and the southern United States, there was usually a free lower class who would find it difficult to compete with slave labour for employment, becoming so impoverished that their living standards would often be as low, if not lower, than that of slaves. (source)

Based on estimates by anti-slavery groups, there were 27 million slaves worldwide at the beginning of the 21^st century, more than in any other historical period, in spite of modern international attention to slavery. (source)