Millions of Africans, who were forcibly transported overseas over a period of about 450 years from the middle of the 15th Century.

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The enslavement of people from west Africa by British, European and African traders, and their mass transportation to the Americas was known as the transatlantic Slave Trade.

A similar slave trade, conducted by Arab and African traders over roughly the same period, saw millions of others transported from the continent's east coast and enslaved in the Arab world.

Slavery had existed for thousands of years, but this period saw the most widespread and systematic form.

How did it begin?

Advances in ship design and navigation enabled European traders to travel reliably to Africa.

The Portuguese were the first to begin capturing Africans and taking them back to Europe as slaves.

Spanish traders took the first African slaves to America in 1503. Over the next century the slave trade developed as a lucrative commercial system.

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Traders used the money to buy raw materials such as sugar, cotton, coffee, metals, and tobacco, which were shipped back and sold in Europe.

By the end of the 18th century Britain had come to dominate the trade, with around 150 slave ships leaving Liverpool, Bristol, and London each year.

How many people were enslaved?

A database compiled in the late 1990s put the figure for the transatlantic slave trade at more than 11 million people, but numbers are still contested.

The total number taken from eastern Africa and enslaved in the Arab world is considered to be between 9.4 and 14 million. The figures are uncertain due to the lack of written records.

More than a million people are thought to have died while in transit across the so-called 'middle passage' of the Atlantic due to the inhuman conditions aboard the slave ships and brutal suppression of any resistance.

Many slaves captured from the African interior died on the long journey to the coast.

On the plantations, life expectancy was short because of poor diet and the back-breaking work. Slaves were branded with hot irons and punishment for trying to run away was whipping or execution.

What was the effect on Africa?

The forced removal of up to 25 million people made Africa's population stagnate or even decline during the slave trade, historians believe.

Some have argued that some African kingdoms were more socially and economically advanced than many European countries before 1500.

In the 14th century, the West African empire of Mali was larger than Western Europe, and reputed to be one of the richest and most powerful states in the world.

Historians continue to debate how and why African kingdoms and traders became so actively involved the slave trade.

Some suggest that the demand for free labour from Europe and the lack of a wider concept of African "identity" at the time allowed slavery to flourish.

Who profited from slavery?

Merchants in Britain, America, Europe and Africa became very rich from the slave trade.

The trade also created, sustained and relied on a large support network of shipping services, ports, and finance and insurance companies, employing thousands of people.

New industries were created processing the raw materials harvested or extracted by slaves in the Americas. Plantation owners profited from the free labour provided by slaves.

The slave trade contributed significantly to the commercial and industrial revolutions of the 18th and 19th Centuries. Cities such as Liverpool and Amsterdam grew wealthy as a result of the trade in humans.

How did it end?

The movement against slavery began in the late 18th Century.

Thomas Clarkson worked against the trade for more than 50 years, travelling Britain to organise meetings and distribute abolitionist literature. He pioneered a string of tactics - including boycotts of goods - which are still employed by campaign groups today.

The publication of "slave narratives" from writers such as Olaudah Equiano helped to change public perceptions of slavery.

British MP William Wilberforce campaigned vociferously against the trade for 35 years and is often given much credit for the parliamentary act banning it in 1807, and the legislation which later freed and gave rights to slaves in British territories in 1833.

While the 1807 act made slave trading illegal on paper, it took a further 60 years of dedicated Foreign Office diplomacy and Royal Navy enforcement to finally eradicate it.

Are there still slaves today?

Although slavery is illegal in every country, it still exists in many parts of the world.

In A Persistent Evil: The Global Problem of Slavery, a report published by the Harvard International Review in 2002, Richard Re suggested: "Conservative estimates indicate that at least 27 million people, in places as diverse as Nigeria, Indonesia, and Brazil, live in conditions of forced bondage"

While this figure is far higher than the total transported during the historical slave trade, it represents a far smaller a proportion of the current global population.

Modern slavery is often more complicated than "chattel slavery" - where one person simply 'owns' another as their material possession.

Practices which amount to slavery include sex trafficking and bonded labour, where a person's work is 'security' for a debt which they can never repay.