Reconstruction failure, Jim Crow institutionalized which was the ultimate inspiration for the Nazis to model their claimed superior race society after.

The US helped to found and popularize the Nazi party. Ford and other industrialist literally bank rolled the Nazi empire. Ford built factories in Germany and let them keep the profits. Nazism was very popular in the US because its policies were based off US policies.

Hitler was inspired by the way the US genocided the Native Americans. This is where the Holocaust came from. When Hitler initially decided to expel the Jews wealthy industrialists lobbied the US government not to take them in. They helped stroke anti-Jewish sentiment in Europe and ensured that no other country would take them in.

This lead to the final solution. IBM and other US companies gave material support to the Nazi. Those numbers tattooed on Jewish prisoners were from a census system IBM developed. Later, they used their computing power to figure out how many jews to ship from the ghettos to the death camps without backing anything up. Basically they handled the logistics of the Holocaust.

Hiring of Nazis after WWII, after inspiring them before WWII.

Don't leave out Unit 731, where they did shit that would make the Nazi's look like Jr high science experiments by comparison...who were given the exact same deals as Paperclipped Nazis

Don't forget that the US government gave Joseph Mengele a new identity. the Angel of Death... got a kiss on the lips, lots of money, and a good luck from America.