Good work, Becky!  Armed with that information, I was able to find a little more.  Edward Madden (lyricist; b. 1878) and Theodore F. Morse (music; 1873-1924) seem to have been particularly active in the first decade of the 20th century; the  Lester Levy Sheet Music Collection  has a number of their pieces, chiefly comic or sentimental songs, often dealing with love, war and the like.  Other examples are at  Historic American Sheet Music.  Madden wrote the lyric for By the Light of the Silvery Moon, incidentally.

It seems that the "Irish" connection may perhaps result from a 1993 record, Peace Together, made by an ad-hoc assembly of performers including Peter Gabriel, Sinead O'Connor, Feargal Sharkey, Nanci Griffith and others, intended "to interpret songs that deal with how young people cope in the confrontational environment of Northern Ireland."  People may subsequently have assumed that the song was intended to refer to that situation, but they can't have listened to the words very carefully!  Madden and Morse were credited as writers on that record, too.

Looks like the American Civil War is the one, then.

Malcolm