Some additional questions,
How was is viewed at the time of release?
How did politicians, activists, commentators, etc view it, or try and use it?
Thank you guys so much for looking at this question, I'm having a hard time finding any info on this classic movie. My usually good google skills are failing me, as all I can find other than wikipedia and IMDb are top ten lists, or articles using "The good, the Bad, and The Ugly" as an expression. Ask Historians is a fantastic resource and I figured you could help more than /r/movies, which didn't help much.
It might help if you provide some additional context to your question- i.e. the history of what? Are you asking about how historically accurate the uniforms are? The firearms? The medical care provided to soldiers?
As for your two bulleted question items: it's been awhile since I've seen the film, but I have seen it many times and remember it as a human story that just happened to be a period piece (really in an anecdotal way). There was no political statement to be made by the director or the producers within the narrative, whether it be about the Civil War or something else entirely. I searched online for any discussion of underlining themes (other than the obvious human elemental themes of greed and desperation in the film) and came up with nothing. For what it's worth, Roger Ebert's revisionist review is (as always) an insightful and interesting read on the movie.