To rival the white slave trade market controlled by Muslims of The Ottoman Empire , European countries sought out slaves from other countries. They couldn’t get white slaves because the ottomans took over everything.

Portugal was the first country to engage in the Atlantic slave trade. They went to Brazil and enslaved indigenous people, and then they made slavery deals with West African countries who were already trading and exchanging slaves...Other European countries followed, and it evolved from there.

Also, one thing that people don’t talk about is that there was this huge technology leap with navigation and sailing. Prior, European countries did not have the boats that could handle the waves of the ocean so they could sail to far away continents and countries.

However, The Arab Slave trade of both whites and blacks is something that never gets talked about , but should. They were africa’s first enslavers, and they enslaved millions of Caucasians from European countries for 7 centuries!

So you can say the Arabs started all that shit, the market, monetary value , in and out of Africa and in and out of Europe....and the Europeans expanded off it.