OTL United States, ironically most pronounced in the Southern States, is known for its intense nationalism especially among its right wing compared to other industrialized democracies. My goal is to have the U.S., in the 20th century, do something horrible that shames its population and is toned down some. A good idea for this would be for the U.S. to fight a war, but resort to open genocide{imagine a Congo conflict that makes Vietnam look tame, and a certain ethnic group is seen as worthy of death for being communists{and are compared to monkeys}} and lose said war(it cannot lead to a situation where the U.S. denies said genocide). Bonus points if there are laws demonizing genocide denial:including a much harder Civil Rights Movement that makes teaching the Lost Cause punishable at the federal level by a fine or a year in prison, and the flag is taboo to show). What I mean by nationalistic is saying "We are the best in the world" and all the flag flying, which is not acceptable in TTL.