The Holocaust represented perhaps the greatest failure humanity has ever known. It featured the combination of technical brilliance and bureaucratic efficiency, but dedicated to the most evil of all purposes. This really is the greatest failure of humanity that I can think of.
In the 19th century, educated people, whether they were Hegel in philosophy or Darwin in biology, or anthropologists, were all convinced that humanity evolves, that humanity climbs a ladder of excellence and civilisation. They believed in the newer, the better, that everything that is old is primitive, and that was a fatal act of hubris on the part of humanity. They thought they knew better than all previous generations and they didn’t realise that they were carrying with them the old demons of fear and resentment and hate and desire for revenge.
The 18th century was a century of reason and peace but the 19th century was a century of nationalism, racism, and ideological warfare of the most horrendous kind and hubris did lead to nemesis. When human beings think they are more than human, they end up by being less than human.
Don’t forget it was in 1879, I think, that Nietzsche said for the first time, “God is dead and we have killed Him” and a mere 60 years later, people were busy trying to exterminate the people of God. That’s what happens if you think you know better than all previous generations; you sink to the lowest depths.