I propose a Theory that the reason Humanity has, and continues to struggle with slavery is because...dah, dah, dah...(key dramatic music)...
Slavery, is in our DNA
We, (Humanity) were genetically engineered to serve as slaves for the Anunnaki.
On the surface, this Theory appears to be completely unbelievable.
Follow the breadcrumbs that I have left inside for a fascinating story reaching from ancient times to modern, and then draw your own conclusions.