A slight difference in cultural heritage

I was watching the Ken Burns series on the Civil War (thanks to Netflix), and several times I caught myself wondering about the background music. About three times I had to remind myself that wasn’t “God Save the Queen” they were playing. What’s the name of the American song that uses that tune? “America Tis of Thee” or something? The more puzzling one is that a tune that I identified as Billy Bragg’s song “There Is Power In a Union”, which is about labour unions and hardly appropriate to a show about the Civil War. But I got to wondering – the chorus begins “The union forever”, and I wondered if it was originally a song about the Union in a “Union versus Rebels” rather than in a “union versus management” sense. That would make more sense. A little googling showed that I was right, it was “The Battle Cry of Freedom”, and the iTunes Music Store has several versions of it.