The story is given by Masato Sakurai in thread 48667: Kingdom Coming
The song was first performed in Chicago in 1862 by Christy's Minstrels.
That thread also mentions the sequel, "Babylon is Fallen."

At the time the song was written, the dialects of poorly educated whites, both born in America and immigrants from the British Isles and Europe, as well as the blacks, were common. The dialects of the whites, because of superior educational opportunities, disappeared more rapidly; moreover they appeared less frequently in printed matter except in diatribes against certain immigrant groups.

Digressing- "De" and "dat" persist in white accents in North America, especially among the French, because of their difficulty with "th." The soon-to-retire prime minister of Canada, Jean Chretien, like many other Canadians of French origin in (officially) bilingual Canada, never overcame the problem and in western Canadian newspapers (such as the Calgary Herald of right-wing bent), is represented as saying "de" and "dat" in political cartoons.