Norman Lear and the writers of the US sitcom "All in the Family" had Archie Bunker explain the answer to this question to his son-in-law Michael Stivick (a/k/a "Meat Head") when he said "Everybody knows it was the Italians who invented Polish jokes, because they wanted to get the heat off of themselves." "All in the Family" was the top-rated sitcom in the US in the early 1970s, so it is very easy to pin the blame for all the Polish jokes in the US in the 1970s on Archie Bunker.