What if someone went in the opposite direction? The American Revolution fails (it wasn’t a sure thing — it’s easier to find a path for failure than to imagine the Confederacy winning) and in 1833 slavery is abolished throughout the British Empire. The southern colonies reject compensation, declare independence, and the troops of the northern colonies plus the iron fist of the Royal Navy descend on the south with fire and sword. Slave rebellions are fed by British arms. After the carnage ends, free Black governments are established in the southern colonies to reflect the will of the people (a quick look at 1830 census data show states like South Carolina were majority Black). Southern rebels flee to Mexico, where they work to establish new power. The southern colonies rebuild, eventually gaining independence after the North American Union and Quebec get theirs in the late 19th Century. And the sun shines brightly on the British Empire when war breaks out in Europe in the early 20th Century and North American troops arrive to finish it early.
Or (new timeline) say, the Empire of Benin stayed strong and kept European imperialism out of Africa (central Africa, anyway)?