Butch,

Using the word Celtic is just needlessly confusing the issue. Sweeney was Irish, not Celtic.

The banjo is an African instrument.

If people wish to know the history of the black faced minstrel shows, they need to know their US immigration history. There were several strands of black face minstrel shows, including the New York/Bowery based shows, and the San Francisco shows. Both cities had substantial Irish immigrant populations, who initially made up the companies which performed the shows. After about 1870 or so, in New York particularly, the companies' immigrant population shifted to become Eastern European Jews performing black face.

Nary an Englishman in the lot, save for Daddy Rice, the man who is said to have invented Jim Crow.