I find it more interesting why the germans became nazis and not other countries. In essence, I think it comes down to the strong value place on both nationalism but equally science and rationalism in Germany. Because there was really nothing in the nazi ideology, anti-semitism, racism etc, that wasn't found in every single other country at the time.
Blatant racism and classifying races and ranking them was the norm at the time. Lots of nazi scientists like the devil Mengele had close ties to the US. I even believe Mengele was an honorary doctor in some US university.
As for why anti-semitism? That was also very common. Henry Ford was a big anti-semitte, as in major anti-zionist. The US was also extremely racist towards blacks at the time. Before WW2 a lot more blacks had been killed due to racial hatred in the US than jews in Germany. But Germany had a lot of jews, the largest population in the world, and there was this idea that the jews had sold out germany in WW1 by getting the US involved in return for Israel. This is somewhat documented by the
Balfour declaration, back then everyone knew full well that the Rothschilds were the de-facto leaders of the world jewish community, hence why the Balfour declaration - a british signatory signing over Israel to the jews - was made out to Rothschild.
Things like these led the germans to believe that international jews had used Germany for their own zionist purposes. This idea is called the 'dolchstoss legende' or the stabbing legende, as in stabbed in the back.
Is it true? Probably not, but who knows.
In any case, after that the general sentiment was that the jews were a foreign power within Germany, sort of like how muslims are perceived now.
As for the Holocaust and all that, I believe it has something to do with the german mentality. The Japanese did similar very un-emphatic things and I've always though they reminded me of the germans.
The large majority of germans were just nazis because they saw germany rise again after having been - unfairly - singled out for retribution after WW1. That mistake, the US did not commit again, and therefore came the Marshall help and such things.
Naturally, knowing what we know today, nazism is horrible, but the general ideas of nazism at the time were not very controversial only the scope.