I have recently come to the conclusion that Stephen Foster's song Hard Times is the second greatest American song every written (the first is, of course, Summertime). Written by Stephen Foster in 1854, and popularized in the Civil War, it is quintessentially American, both musically and thematically. And it's inspired so many other tunes. Here, the original performed by the Kate and Anne McGarrgile, and two new songs, which I like to think were inspired by the original.
(UPDATE: this Pokey LaFarge video is disturbing, but the song is awesome, so I'm keeping it up.)