seriously? You think humans learn from history. Humans take part in ethnic cleansing all the time. What was learned from the Holocaust?
You have to look at history a little more analytically than that. For this purpose it's not possible to separate the Holocaust from WWII.
Documents captured after the war revealed that the Nazi government realized that even a victorious Third Reich would not be able to get away with exterminating the Jews in peacetime, therefore they accelerated their efforts to complete the job during the war. This is the phenomenon known as "the fog of war," writ large. Very, very, very large.
What we learned from WWII is that war makes things like the Holocaust possible. Sixty million people died in WWII. (There are various estimates but this one is pretty reasonable.) A full two percent of the population of
the entire planet. That includes not only battle casualties but second-order effects such as Russian civilians dying from the destruction of their infrastructure in wintertime. In that context it's easy to see why the Germans thought that the world would accept their postwar explanation that another six million Jews, in addition to the first six million, were simply war casualties.
Which means that, in a sense, they
were war casualties.
If the world were not at war, they would not have died!
We learned a lot from WWII, and the Holocaust was only part of that lesson. It was the bloodiest war in human history, and since then every nation has been reluctant to get into a war of that scope again. Only a handful of wars in the last sixty years have body counts exceeding
one million. And only one, the Congo Civil War, ran over two million; unfortunately it was closer to five million but that's still a whole order of magnitude smaller than the war that was raging when I was born.
Countries are reluctant to come to each other's aid for fear of starting a regional war that will snowball. It's sad that nobody tried to rescue the people of Tibet or Georgia or Palestine or Darfur, but does anyone here think for two seconds that if a major power had stood up to China or Russia or Israel or whoever the hell is calling the shots in Sudan (my wife says it's the Chinese), that it wouldn't have blown up in our faces?
We Americans recently overthrew our government--in the peaceful, democratic American style of holding an election but nonetheless it was intense--largely because we don't want to fight a war in the Middle East.
That's what we learned from WWII, and the Holocaust just gave it some clarity.