African Slave Trade

Slavery had a long history in Africa. However, these slaves were usually prisoners of war, and had to some extent legal rights. Slavery wasn't permanent, and was almost never inheritable.
However, Europeans had begun to set up trading posts around Africa, and would trade guns for slaves.

Cycle into slavery

Africans would sell prisoners of war to Europeans in exchange for guns ->
Africans could get more prisoners of war ->
Repeat

Racist Ideas

To morally justify the slavery of Africans, Europeans adopted thoughts and ideas to convince themselves that Africans were "inferior" to the "superior" white people. One way this justification happened was the use of the Bible.

Beginning of Transatlantic Slave Trade

The Spanish Empire lacked labor in the new world. The Native American slave labor wasn't good enough, since the Native Americans would keep dying to disease. Instead, Spain turned towards African slave labor, since Africans weren't as vulnerable to these diseases. Thus started the Transatlantic Slave Trade.