I think this is quite a narrow view of the history of slavery:

Of course it is an abomination and the embodiment of true human evil, but it is important to consider that slavery is pretty much as old as humanity itself and was a nearly ubiquitous practice across cultures. Britain was the first modern civilization that not only outlawed this >10,000 year old institution but also expended resources to enforce its destruction and take a stand against its immorality. Britain forced even forced African countries who were benefiting immensely from the international slave trade to ban the practice (see Benin). The king of Benin “The slave trade has been the ruling principle of my people. It is the source of their glory and wealth.” Britain blockaded Benin into submission over slavery. Interest fact: Mauritania outlawed slavery in 1981...

The Atlantic slave trade was nothing novel, it was another iteration of the international slave trade. Slavery was a big business well before Britain got into it. Britain did reap benefits of slavery, although not nearly as much as Portugal, while simultaneously Britain is largely the reason we don’t have legal slavery today. It isn’t black and white.

I would recommend reading the chapter on slavery in “Black Rednecks and White Liberals” by Thomas Sowell