Such riots were caused by the greed of the Portuguese for Indian spices for which they had nothing to exchange. In Africa, European expeditions will be the start of the transatlantic slave trade. The Portuguese imported African slaves to work on their sugar plantation. These slaves were more or less considered non-human due to the treatment they received from their (European) masters. They were lined up with coffins around their necks and whipped as they made their way to the slave ship for transport to Europe. The mortality rate was estimated at 15 percent. When slaves arrived in Europe, they were sold to the Americas. High demand for labor in the Americas led to the sale of African slaves. This caused the triangular slave trade between these three continents: Africa, Europe and the Americas. They worked on plantations and were considered commodities because they were sometimes auctioned off for buyers. They were also marked to indicate where they belonged and who their master was. The slave trade led to the decline and fall of African kingdoms. Many houses collapsed due to European contact with many African empires. Congo King Nzinga Mbemba politely expresses his concern about the slave trade to the King of Portugal by writing how his kingdom is being destabilized by taking and selling his people as