Tried asking this on the Reddit history pages, immediately removed for asking for a "basic fact", meanwhile sourcing is near impossible to find.
Ive been trying to find more sources on the origins of the racial identity construct, particularly in the development of widespread white supremacy, and how the "white" identity developed. In my research, it has seemed very clear that it developed in conjunction with the Catholic Church's rise to power at the continental scale. In this same location, fertile birthing grounds for settler-colonialism, capitalism, and white supremacy. Any recommended reading on the subject would be greatly appreciated.
Furthermore, as the title stated, I am looking for the earliest recorded instances of one peoples inflicting subhumanization behavior on another. Obviously conflict between different groups of people traces far back before recorded history, but I am very interested in finding when a group first identified as "pure" human, while declaring all those without said traits subhuman. I have a feeling there must be some Marxist text on this, so if anyone knows it I'd love to see it.
Selfish plug to the research I've done thus far if anyone wants to check it out
It's really not. Slavery at least as far back as Aristotle has had justifications based on the animal nature of slaves. This involves things like saying that some people are natural slaves to be ruled (dominant form of rationalizing slavery and anti-democracy in the west for 2.5 thousand years at this point). What makes up a natural slave changes over time though according to cultural and material conditions.
Marx is in this tradition too, just his natural slaves are mechanical machines, and all people are free beings. That's one of the libratory aspects of industrialization.