Slavery in Europe started a long time ago. The main slaves used in Europe are American Indians and Africans.The first reason why Europeans use slaves was because of the Mercantilism. It is the theory that wealth is created by trade. A large part of Africa is colonized by the europeans, and as Africa is close to Europe, it is very easy to catch slaves from there.
Secondly, due to Mercantilism, the europeans wanted the enslaved people to work in mines and on tobacco plantations in South America and on sugar plantations in the West Indies so they can sell these things (tobacco and sugar) back to the colonies and export more products than they import. Millions of Africans were enslaved and forced across the Atlantic, to labour in plantations in the Caribbean and America.
Thirdly, Europeans thought that black skinned people could be said to be a "sign from God" of something evil. In 1899, the poem The White Man’s Burden was written by Joseph Rudyard Kipling. In the poem, he claimed that the slaves are burdens of the white mans and are obligate to work for white men forever.This manifests the general attitude of the Europeans towards the slaves: white man has a moral obligation to rule the non-white- peoples of the Earth.