Apologies for all the questions, and further apologies if these have been asked before. I don't know much about WWII but am trying to learn more, and I get the feeling that my high school era history classes were less than truthful about America's involvement during the war. To specify my context for these questions:
1.) I've heard claims that the Nazi party's treatment and hatred of Jews and other minorities was, partially, inspired by American racism and Jim Crow laws. I knew nothing about this! Is this true?
2.) I've always just assumed that we fought the Nazis in WWII because... well, they were evil. But recent discussions with others have shown me opinions others hold that America didn't fight the Nazis for ideological reasons or because they wanted to stop genocide. If this is true, what was the American government's real motivation for fighting in WWII against the Nazis?
3.) Going off of the last question, did America and its citizens even know about the Holocaust and its atrocities during WWII itself, or did our knowledge of these things come from after the fact?
These are a lot of very different questions to answer all at once which (in my opinion) aren't actually as related as it may seem, I'm going to tackle only #1.
Nazi hatred of Jews and other minorities was not particularly inspired by the USA, rather by historical reactionary currents in Europe itself. Anti-semitism had a long and storied history and they picked it up from there, ditto for Roma hatred. Anti-communism and homophobia are more obvious and self-explanatory - they were groups vilified throughout the world, the Nazis just took it to a genocidal extreme.
Where they were inspired by the USA is in how to 'deal with' the people they hated. They didn't consider the US to be an ideal model for the racial state they wanted to create, rather just the best extant example of the sort of thing they wanted to do.
It was a country that Hitler believed had been colonized by 'Germanics' who'd conquered the land through genociding its native people, and who used their 'superiority' to oppress other 'races' through laws like Jim Crow. So it was an example that what he wanted to achieve was possible, proof that it could be repeated and improved upon. He considered it an important example to be studied for what he wanted to do both to Jews, Roma etc and to Eastern Europeans (who he sometimes called 'Redskins') in the places he wanted to conquer & colonize.
In Mein Kampf, regarding American race laws, he wrote:
There is but one state in which at least progress towards good citizenship laws is noticeable. Of course, it is not our model German Republic, but the American Union at least partially tries to use reason. By refusing immigration on principle to elements of poor higene, by simply excluding certain races from naturalization, it professes in slow beginnings a view that is like that of our Volkish state concept.
When the Nazis finally implemented their own race laws 10 years after that was written, they naturally looked towards the US for ideas, and some Nazi lawyers even visited the country and studied them & their effects intently. They also studied South Africa, but the US influence was most significant. Nonetheless, they didn't literally copy the laws 1:1, but they were an important predecessor and taken as a sort of 'proof of concept' that such laws could work - especially since in Hitler's imagination the USA was through some magic dominated not simply by whites but specifically by 'Germanics' who were just like him!.
So the Nuremberg Laws & other Nazi race laws were certainly inspired by the US example. Would they have passed such laws anyway? Maybe. But it was very important for them that there was another country that had shown, at least a bit, that such a system could be implemented.
If you're interested in something a bit off topic from your original question, (which I think you may be judging by the pure quantity of questions you asked here!!), I have another old reply that goes more into how top-level Nazis and Hitler especially also looked towards the US in a very similar way regarding its conquest/genocide of Native Americans.