The correct answer to this open question is the following.
What are the risk factors and warning signs that made the atrocities of the Holocaust possible?
The consequences of World War I in Germany left unhealed wounds. There was too much pain, suffering, and destruction. This created a lot of instability in the region.
The Weimer Republic that had started after World War I have failed the German people who were desperate due to the poor economic conditions they lived in. Extremist movements and ideologies came into existence such as Fascism, National Socialism, and Communism.
This scenario was the right one for people like Adolph Hitler could be name leader in Germany, knowing that he had these extreme racist and supremacist ideas.
What steps can be taken today to ensure that such inhumanities never happen again?
Humanity has to be aware and closely follow any extremist ideology in any country on the planet, in order to prevent another horrible event like the holocaust.