The discovery of the American continent led to the flourishing of the black slave trade from Africa. The main slave trade markets were located in Morocco, Algeria, Tripoli, Cairo, Genoa, Venice. The maritime city of Lagos, Portugal, where African slaves were sold, was opened in 1444. Slavery in various countries of the world still exists today. The number of people in slavery is said to be almost 25 million. Most countries in the world signed the UN Convention on the Prohibition of Slavery in 1948. Slavery in one form or another exists in Sudan, Mauritania, Ghana, Thailand, China, Brazil, and many other countries. Human trafficking is a profitable business.