According to Wikipedia, "Soldier's Joy" is one of the oldest tunes. The tune appeared in the late eighteenth-century and by the nineteenth century, it was published in numerous books of fiddle tunes, usually classified as a reel or country dance.
According to documentation at the United States Library of Congress, it is "one of the oldest and most widely distributed tunes". According to the Illinois Humanities Center, the tune dates as early as the 1760s. The tune has an upbeat tempo and catchy melody; however, the term "soldier's joy" has a much darker meaning than is portrayed and came to refer to the combination of whiskey, beer, and morphine used by Civil War soldiers. Source: Library of Congress.
"Soldier's Joy" was a popular fiddle tune that often accompanied a soldier receiving his monthly pay in the 1860s. Source: Danny Lee Ramsey.