Here’s a brief suggestion (I’m hoping to expand my response into a separate article soon): White people who bring up the Jewish Holocaust without mentioning the first two American Holocausts you cite don’t do so primarily because of the identity of the victims but because of the identity of the victimizers. The Nazis were the bad guys. We fought the Nazis. So it’s acceptable to bring up the Nazi concentration camps as an example of genocide. Only the most deluded would claim that Andrew Jackson or the leaders of the Confederate States of America were the good guys (okay, so there are a lot of deluded people out there). But on a hypothetical SAT History exam, most white Americans would acknowledge that The Trail of Tears and the enslavement of Africans were not models of good behavior. “These things shouldn’t have happened, but hey, that was a long time ago.”
The reason white Americans prefer the Jewish Holocaust as the exemplar for human barbarism is that in that case they don’t see themselves as the bad guys.
How many textbook accounts of the Jewish Holocaust cite the story of the MS St. Louis, a ship consisting mostly of Jewish refugees from Germany that was denied entry into the U.S. and Canada in 1939, which resulted in the deaths of about 254 Jews, the majority of whom were sent back to France, Belgium, and the Netherlands, where they were later captured by the Nazis and sent to concentration camps?
This slightly more subtle form of denial (“these bad things did happen, but we’re not responsible for them”) is, I’m afraid, human nature. Many Germans (who are not Holocaust deniers) and Poles find it unpleasant to dwell on the atrocities of WWII. Some French citizens would like to forget about French collaboration with the Holocaust (and don’t even bring up Algeria).
Why is the Civil War portrayed as a tragic war of brother against brother, when the savage Fort Pillow Massacre paints an entirely different picture?
Why was there not a major American western about genocide against native Americans until Cheyenne Autumn in 1964?
I’m afraid that if we can’t see ourselves as the good guys in a particular historical account, we’d rather just forget about it.