The forced migration of millions of Africans to diverse areas of the Americas had wide-reaching implications that are still being felt to this day. Demographically, economically, and culturally, the legacy of slavery was felt from Africa to Europe to the societies of the New World.

The trans-Atlantic slave trade seriously affected the demographic growth of many African societies directly, and had a more subtle impact on many others. As stated above, the disruption caused by the forced migration of many young men from villages meant a shift in marriage patterns as the number of marriageable men declined. For many societies on the West coast of Africa during the trans-Atlantic slave trade, populations either declined, remained constant, or had very little growth, usually suffering a varying disproportion between the numbers of men and women. For the Upper Guinea Coast, for example, slave exports were great enough during the latter half of the eighteenth century to reduce the regional population, and halt growth into the first decade of the nineteenth century. During this period the ratio of men to women dropped to below eighty men per one hundred women. In those societies where there were few slaves taken, population growth was more constant, although demographic effects of the slave trade were still a factor. The disruption caused by inter-tribal warfare and the capturing of slaves for the European market often heightened the effects of natural disasters such as disease or famine. The effects of a famine could be greatly magnified if fewer people of a village were available to produce food, and a higher death toll as a result would reduce the population even more. As well, the continual interaction between villages brought about by the migrations of slaves across Africa facilitated the spread of diseases, further disrupting the growth of populations. These disruptions were especially devastating for the region of Angola, where an increase in slave exports in the nineteenth century resulted in an even greater decline in population.

It has been estimated that in 1600, the population of Africa stood at about 50 million people, or thirty per cent of the combined populations of the New World, Europe, the Middle East, and Africa. By 1900 the population of Africa had grown to 70 million, but made up only ten per cent of the total combined population. Furthermore, the population of Africa in 1850 has been estimated to have been only about half of what it would have been had slavery and the slave trade not been a factor in African history.

Whereas Africa suffered a population loss, the slave trade to the New World resulted in an increase in the African populations there, both directly from Africa and those who were subsequently born in the Americas and Caribbean. Today, one-tenth of the United States’ population are descended from slaves, and the proportion is even higher in, for example, the British West Indies. Before the revolution in Saint Domingue (Haiti), slaves made up seventy per cent of the population. The dispersal of Africans throughout the New World is directly related to slavery, as they were forced to go wherever labour was demanded. After the abolition of slavery, however, many slaves were left without the resources or means to set up for themselves and were, therefore, unable to move in order to improve their conditions. Freed slaves sometimes wound up working for their ex-masters and mistresses under conditions very similar to those endured under slavery itself.

The demographic impact of the trans-Atlantic slave trade is further complicated by the wide variety of racial mixing which took place both during and after the slave trade. The New World saw a growth of large populations of individuals who were not purely African, European, or Amerindian. The complex classification system developed to categorise such individuals testifies to the size and strength of this new population, which could be found throughout the Americas and Caribbean in almost every occupation and which could be of any social status.