From the middle of the 15th century, Africa entered into a unique relationship with Europe that led to the devastation and depopulation of Africa, but contributed to the wealth and development of Europe. From then until the end of the 19th century, Europeans began to establish a trade for African captives.
At first this trafficking only supplemented a trade in human beings that already existed within Europe, in which Europeans had enslaved each other. Some enslaved Africans had also reached Europe, the Middle East and other parts of the world before the mid-15th century, as a result of a trade in human beings that had also long existed in Africa.
Many of these African captives crossed the Sahara and reached Europe and other destinations from North Africa, or were transported across the Indian Ocean.
The transatlantic slave trade began during the 15th century when Portugal, and subsequently other European kingdoms, were finally able to expand overseas and reach Africa. The Portuguese first began to kidnap people from the west coast of Africa and to take those they enslaved back to Europe.
It is estimated that by the early 16th century as much as 10% of Lisbon's population was of African descent. After the European discovery of the American continent, the demand for African labour gradually grew, as other sources of labour - both European and American - were found to be insufficient.
The Spanish took the first African captives to the Americas from Europe as early as 1503, and by 1518 the first captives were shipped directly from Africa to America. The majority of African captives were exported from the coast of West Africa, some 3,000 miles between what is now Senegal and Angola, and mostly from the modern Benin, Nigeria and Cameroon.
Historians still debate exactly how many Africans were forcibly transported across the Atlantic during the next four centuries. A comprehensive database compiled in the late 1990s puts the figure at just over 11 million people. Of those, fewer than 9.6 million survived the so-called middle passage across the Atlantic, due to the inhuman conditions in which they were transported, and the violent suppression of any on-board resistance. Many people who were enslaved in the African interior also died on the long journey to the coast.
The total number of Africans taken from the continent's east coast and enslaved in the Arab world is estimated to be somewhere between 9.4 million and 14 million. These figures are imprecise due to the absence of written records.
The forced removal of up to 25 million people from the continent obviously had a major effect on the growth of the population in Africa. It is now estimated that in the period from 1500 to 1900, the population of Africa remained stagnant or declined.
Africa was the only continent to be affected in this way, and this loss of population and potential population was a major factor leading to its economic underdevelopment.
The transatlantic trade also created the conditions for the subsequent colonial conquest of Africa by the European powers and the unequal relationship that still exist between Africa and the world's big powers today.
Africa was impoverished by its relationship with Europe while the human and other resources that were taken from Africa contributed to the capitalist development and wealth of Europe and other parts of the world.
The unequal relationship that was gradually created as a consequence of the enslavement of Africans was justified by the ideology of racism - the notion that Africans were naturally inferior to Europeans.
This ideology, which was also perpetuated by colonialism, is one of the most significant legacies of this period of history.
Africa's economic and social development before 1500 may arguably have been ahead of Europe's. It was gold from the great empires of West Africa, Ghana, Mali and Songhay that provided the means for the economic take-off of Europe in the 13th and 14th centuries and aroused the interest of Europeans in western Africa.
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.
When the emperor of Mali, Mansa Musa visited Cairo in 1324, it was said that he took so much gold with him that its price fell dramatically and had not recovered its value even 12 years later. The empire of Songhay was known, among other things, for the university of Sankore based in Timbuktu.
Historians have long debated how and why African kingdoms and merchants entered into a trade that was so disadvantageous to Africa and its inhabitants.
Some have argued that slavery was endemic at that time in Africa and that, therefore, a demand from Europe quickly led to the development of an organised trade.
Others have queried the use of the term 'slave' when referring to servitude in African societies, arguing that many of those designated slaves by Europeans had definite rights, and could sometimes own property or rise to public office.
Africans could become slaves as punishment for a crime, as payment for a family debt, or most commonly of all, by being captured as prisoners of war. With the arrival of European and American ships offering trading goods in exchange for people, Africans had an added incentive to enslave each other, often by kidnapping.
There is no doubt that Europeans were not capable of venturing inland to capture the millions of people who were transported from Africa. In the areas where slavery was not practised, such as among the Xhosa people of southern Africa, European captains were unable to buy slaves.
On the African side, the slave trade was generally the business of rulers or wealthy and powerful merchants, concerned with their own selfish or narrow interests, rather than those of the continent.
At that time, there was no concept of being African. Identity and loyalty was based on kinship or membership of a specific kingdom or society, rather than to the African continent.
Rich and powerful Africans were able to demand a variety of consumer articles and in some places even gold for captives, who may have been acquired through warfare or by other means, initially without massive disruption to African societies.
However, by the mid-17th century the European demand for captives, particularly for the sugar plantations in the Americas, became so great that they could only be acquired through initiating raiding and warfare.
There is no doubt that some societies preyed on others to obtain captives in exchange for European firearms, in the belief that if they did not acquire firearms in this way to protect themselves, they would be attacked and captured by their rivals and enemies who did possess such weapons.
However, some African rulers did attempt to resist the devastation of the European demand for captives. As early as 1526, King Afonso of Kongo, who had previously enjoyed good relations with the Portuguese, complained to the king of Portugal that Portuguese slave traders were kidnapping his subjects and depopulating his kingdom.
In 1630, Queen Njingha Mbandi of Ndongo (in modern Angola) attempted to drive the Portuguese out of her realm, but was finally forced to compromise with them.
In 1720, King Agaja Trudo of Dahomey not only opposed the trade, but even went as far as to attack the forts that the European powers had constructed on the coast. But his need for firearms forced him to reach an agreement with the European slave traders.
Other African leaders such as Donna Beatriz Kimpa Vita in Kongo and Abd al-Qadir, in what is now northern Senegal, also urged resistance against the forced export of Africans.
Many others, especially those who were threatened with enslavement, as well as those held captive on the coast, rebelled against enslavement and this resistance continued during the middle passage. It is now thought that there were rebellions on at least 20 percent of all slave ships crossing the Atlantic.
The transatlantic slave trade led to the greatest forced migration of a human population in history. Millions of Africans were transported to the Caribbean, North and South America, as well as Europe and elsewhere. An 'African Diaspora' or dispersal of Africans outside Africa was created in the modern world.
Those in the Diaspora have often maintained links with the African continent, while forming an important part, and sometimes the majority, of new nations.
Africans from the continent and the Diaspora have sometimes organised together for their common pan-African concerns, against slavery or colonial rule for example, and so over time a pan-African consciousness and various pan-African movements have developed.
In recent years the African Union, the organisation of African states, has recognised that the Diaspora, as well as Africans from the continent, must be fully represented in its discussions and decision making.