I too would like to know the history that underlies the lyrics of this song. Let me explain ...
I recently heard an American girl sing this song in a pub in Oxford, UK (The Half-Moon). She told me that she'd got it from a Silly Sisters (Maddy Prior and June Tabor) CD. I bought the CD on the basis of this song and was not disappointed.
I am now learning the song myself so I can perform it next time I am at a session. I'd love to know more about the events that it is describing. I have lived in Newcastle and also in Scotland so am particularly drawn to it.