I agree wholeheartedly with you that that moving on and connecting as humans is what is needed for the world to live in peace. This should be the goal of all decent people everywhere.I think American racism toward the descendants of slaves is different from the tribalism you note based on differences in wealth, religion, appearance, sports team, whatever. Those have some underlying basis that the 'other' has a chance of winning, of becoming superior, in some sense. But the American slave economy had to include a belief that the slaves had no human soul, that God had condemned them for some reason and that they had no God-given right to hold an opinion on anything. The Christian justifications for continuing slavery were widespread, and just plain evil. This really came into focus as other nations abandoned slavery on moral grounds while meanwhile the US doubled down claiming God's will justified buying, selling, breeding slaves same as livestock.
I think we still have a faint echo of this belief that black Americans have no standing as citizens, in the recent complaints that football players have no right to express a political opinion. Things were more stark 50 years ago, look at any compilation of MLK's speeches for a broader illustration of this concern. Things are better now but the holdouts who cling to their ignorance re racism and all the other tribalisms you noted, continue to be a powerful element of American society. The demagogues who encourage them and rely on their support have no human decency and need to be voted out.