When Simon and Kirby created Captain America, it was a year before Pearl Harbor. Americans feelings were mixed about Hitler and the war in Europe, with many Americans sympathizing with Hitler. So when the first Cap cover came out, with Cap punching Hitler on the jaw, there were death threats made toward Timely comics and Simon and Kirby individually. The mayor of New York assigned body guards to Simon and Kirby.
Of course a year later, the events of Pearl Harbor solidified the American position against the Japanese, and by extension, Hitler.