The governments of countries need to acknowledge the atrocities they've committed, as such helps in preventing them from occurring again. Germany has set the precedent for this, as they go out of their way to take responsibility for the Holocaust. Their schools require students to visit concentration camps to learn firsthand about what happens. Though the US doesn't go this far, honestly, we haven't done anything that bad. And what we have done (for example, the Trail of Tears), we educate our people about.
Now, for a government that's horribly stuck in the past, we have Japan. Many of their people still refuse to acknowledge that the Rape of Nanking ever happened, including much of their government. They love to talk about about how devastating the atomic bombings were, yet they flat-out refuse to mention the war crimes they've committed, many of which are much, much worse than the atomic bombings. For example, Unit 731. In Unit 731, some of the vilest, most inhumane crimes against humanity were perpetuated. Quite honestly, many of the things done there rival and at times are even worse than Dr. Mengele's experiments in terms of brutality. And on whom were these acts performed? Innocent Chinese civilians. Yet the Japanese never mention this.
But you know, America is the most evilest nation ever, and NIHON IS KAWAII~~NYA~~!