How were the west african kingdom involved with the slave trade?

https://socratic.org/questions/how-were-the-west-african-kingdoms-involved-in-the-slave-trade

With the development of the trans-Saharan slave trade and the economies of gold in the western Sahel, a number of the major states became organized around the slave trade, including the Ghana Empire, the Mali Empire, and Songhai Empire. However, other communities in West Africa largely resisted the slave trade.

The transatlantic slave trade began during the 15th century when Portugal, and subsequently other European kingdoms, were finally able to expand overseas and reach Africa. The Portuguese first began to kidnap people from the west coast of Africa and to take those they enslaved back to Europe

during both period congress passed law restricting the civil liberties of american citizen that meet with the overall public support is the one statement that explain the rate scare of the 1920 and 1950 is very similar