The most obvious example is what the jews did to palestines in palestine/israel a few years after ww2. Look at what we did in vietnam/laos/iraq/etc. Look at what the chinese are doing to their minorities. Look at what happened in rwanda. Did we all forget ww2? Of course not.
The idea that we are doomed to repeat history if we forget it is nonsense. The nazis didn't forget about the history of the native genocide in the US. They actually studied it and they learned from it and they improved upon it.
Think about it, neo-nazis want to remember the past just as much as the holocaust survivors. But for different reasons.
As long as people have their creature comforts and are well fed and content, we'll pretend to be civilized and caring and charitable. When that gravy train dries up, we just resort to our natural tribal state.
Nobody forgot the native genocides, but the holocaust happened. Nobody forgot the holocaust, but the rwandan genocide happened.