Suppose the abolition movement fails in Europe and survives until even the late stages of imperialism. If I recall correctly, Britain was still profiting from the slave trade, and only ended it for moral reasons. Perhaps slaver interests win in Parliament. Eventually, the "Scramble for Africa" involves competition over controlling the best slave routes on the African continent.
(Ignore the USA, its development happening as OTL.)
Would slavery's continued survival in the Caribbean, Africa, and (to a lesser extent) Asia affect the world in a major way?