Until the 18th century, few people thought there was anything wrong with slavery. Both African rulers and European traders were happy to trade in slaves.
The slave trade began with Portuguese and Spanish traders taking African slaves to the American colonies which they had conquered in the 15th century. Around 350,000 Africans were taken in this way as slaves to the Americas.
In the 16th century, English pirates started selling slaves to the Spanish colonies - Sir John Hawkins was the first English sea-captain to do this. Other nations looked to his example and soon joined in.
In 1713, the Treaty of Utrecht was signed. Spain gave British slave traders the contract, known as the Asiento, to trade 144,000 slaves a year to Spanish South America. After 1700, the numbers of slaves being transported increased greatly.
Around six million Africans were taken as slaves to the Americas, at least one third of them on British ships. It has been estimated that overall, about 12 million Africans were captured to be taken to the Americas as slaves.
In 1770 approximately 100,000 slaves were shipped from Africa to the Americas. British ships carried about 50,000 of these people.
In 1790 the figure for slaves carried to the New World was 74,000. British ships carried about 38,000 of these people, French 20,000, Portuguese 10,000, Dutch 4,000 and Danish 2,000.
British trading ships took part in the slave trade up until its eventual abolition in 1807.