While the above answer is accurate it is far from complete. European empires and private companies invested in New World exploration. Like any other investment they sought return and growth on the money they fronted for these voyages. The "New World" was rich in natural resources. It also required intensive labor to reap these returns. . So European traders exploited ethnic warfare on the continent of Africa to find this labor. As rival tribes warred the prisoners of the defeated tribes were sold into slavery by the victorious tribes. This led to an increase of ethnic warfare on the continent. As a result tribal tensions increased, which is a factor in the ethnic warfare continued today in Africa. . Another factor was the need for specalized labor. Take the rice industry for example. Growing rice is a labor intensive, highly skilled process. Europeans did not know how to grow rice themselves, so they purchased slaves from areas in Africa where rice was a cultivated crop. . So simple labor needs do not fully answer this question. European investors wanted returns on their capital. This required the Europeans to indirectly increase ethnic hostilities in Africa which increased the supply of slaves. These slaves were used to reap the value of the resources of the New World, and they were also used to bring the skills needed to further the benefit the natural bounty of the Americas.