Let me first say that racism is an ugly stain not just on America but on all of humanity. Then let me turn around and say that it is as natural as breathing. Yes, indeed, it is. It is called tribalism. My tribe is all goodness. Your tribe is all evil. It’s just the way humans are hardwired.
Basically it’s the negative offset of why people with much in common — race religion, ethnicity, town, nation, or even high school when it comes to sports, band together for the common good.
In fact if you were to alternating put red and blue armbands on random folks entering some physical location, with all else being equal, those with red armbands would soon be finding fault with those of blue armbands and vice versa. Difference of any sort matters big time.
And because of the universal law of probability balance it is impossible for collective humanity to escape this negative offset of the tribal instinct of which racism is only one example of the commonalities that set groups of peoples apart. Alas, what binds us together for good purpose also triggers our destructive impulse. This is why war always follows peace as sure as the sun rises in the East.