When was America great ?

[*Synric*]

I would answer late 1800s into the early 1900s (Between the Civil War and the Great Depression) the US was an industrial giant during this period.

From around the 1960s to the 1980s a plastics boom, the beginning of the boom in Silicon Valley would be a decent answer I guess. The Automotive world was big in the 1950s -1980s too...