The United States is often described as a "melting pot" -- a land where people from different cultures come together to into one American people.

To clarify, when I say "Myth", I don't mean something that is untrue or that did not happen. I use "Myth" in the sense of "a idealized story we tell about ourselves."

In my research, the popular sentiment at the founding of the republic in the late 18th century could hardly be called pluralistic or a "melting pot." The term was already fully in place by the mid 20th century. So where did it come from?

I assume it has something to do with the Northern European immigration wave of the early 19th century because they were more accepted by Americans at the time than subsequent, less homogeneous immigration waves that came later. This is merely a guess, however.