Thus America produced a composer (5)
I believe the answer is:
sousa
'a composer' is the definition.
(I know that Sousa is a composer)
'thus america' is the wordplay.
'thus' becomes 'so' (synonyms).
'america' becomes 'usa' (synonyms).
'so'+'usa'='SOUSA'
'produced' acts as a link.
(Other definitions for sousa that I've seen before include "American composer known for marches" , "Composer of "The Stars and Stripes Forever"" , "John Philip -, composer of famous marches (The Stars and Stripes for Ever)" , "John Philip --, American march composer" , "he produced the Washington Post" .)