Can you clarify your question a little bit? The 1920s was a time of economic prosperity in the US, and on the world stage, America's reputation was on the rise after WW1. The 1920s also saw the rise of popular entertainment media like radio, film, and pop music that not only took the world by storm but continues to be one of the country's major exports overseas.

I can't think of a single area -- except perhaps in the realm of civil rights/race relations and the failed policy of alcohol prohibition -- where the USA was on the decline in the 1920s.