Haha wow..

Racism and orientalism and colonialist thinking, yes. But also: theology!

Abyssinia, as you've probably googled, was an antiquated/orientalized name for Ethiopia. The Ethiopian Church (or Ethiopian Orthodox Church, as it's often known today) is one of the oldest in the world...and was unceremoniously kicked out of the Church-of-the-people-publishing-that-Bible in 451.

Christians spent the first 500 or so years of Christianity arguing about whether Jesus was fully God, and if so, in what way was he simultaneously fully human and fully God. The 451 Council of Chalcedon dealt in particular with the second one: how different regional churches/theologians described Jesus' nature(s) as fully human and fully God.

My favorite visualization here is:

Most of the northern/western (future Catholic-Protestant-Eastern Orthodox) churches and theologians favored a human nature and a divine nature as two ropes twisted around each other and superglued together at the atomic level. Impossible to separate, but separate.

Churches and theologians like Ethiopian ones, on other hand, used language that more resembles the two sides of a flat shoelace. Also separate but impossible to separate, just in a different way.

Today, most people wouldn't really perceive a difference between the two views. In 451...not so much. The people in control of the Council more or less declared that they (two ropes) people were correct, and the future Coptic, Ethiopian, &c Churches (shoelace) were wrong. Rather than accept the other views, the eastern/southern churches became The Church from their point of view.

And--of course--the northern/western churches also became The Church from their point of view. And stayed that way.

Nineteenth-century racism and imperialism also swayed the publishers of that Bible towards trashing the Ethiopian Church so wrongly. ("Nondescript heathens"...) But even so, the roots of a theological disagreement--which most people today would say is not actually a disagreement at all--go way, way back.