It wasn't a great deal of triggers that lead to the popularity of the Nazis and it is still something that is occurring, albeit in much smaller scale to this day. Deep recession & poverty, jealousy of immigrants, dented national pride. Ring any bells with the likes of Bosnia? Iraq? The corrupt elements of Africa? Genocide didn't stop with the Jews/Gypsies/non-Arian races at WWII (remember, the Holocaust wasn't just Jews being killed)... but seemingly even the Jews haven't learnt from what happened to them, arguably they're inflicting the same hate they received upon their neighbours in Palestine.
Look at the hate the BNP spread, yet their support is growing right here in the UK, where people in our lifetime died to protect us from the very same disgusting attitude.
It's only through learning we fully understand what we could not be there to witness ourselves. These memorials, museums, etc stand as a cold reminder and education of what happens when hate is allowed to rule and sacrifices have to be made to overcome.