Virtually all Jews fled to the USA prior to the Immigration Act of 1924, which among other goals was to block Jews coming to the USA. As murder and increasing slaughter of Jews became worldwide, Jews were trying to flee to Israel, despite Britain trying to block the number of Jews coming to Israel.
By 1938, Jews were desperate to get out of Europe and Britain proposed a small Jewish zone, smaller than present day Israel, and for all the rest being exclusively for Arabs. The Jewish Council agreed, but Palestinian Muslims riots, demanding that Jews do not have 1 inch of land and instead that Jews be evicted. Britain withdrew it's proposal.
This left nowhere for European Jews to go, resulting in the murder of 1/3rd of all Jews in the World, 6 million, in the holocaust. However, the murder and oppression against Jews was worldwide, other than Britain attempted to maintain law and order in what is now Israel, so those few who could make it there were relatively safe.
Few American Jews have any ancestry or direct linkage to the holocaust and have been safely within the USA so long they have no memory of the reason their ancestor's fled to the USA, just like many others of different ethnicity who came to the USA to escape do not.