Thanks. If you type in 'Black Regiments Civil War' on internet anyone can see that black soldiers had a much more extensive involvement than the film but yes I based the picture on the famous battle sequence at the end of Glory. The obvious picture title would have been Glory.
Yes I did the picture on sand dunes like in the film. Strangely I always remember the union flag at this time as having an interesting circular arrangement of stars but I did not have that flag and could not be bothered to specially produce one. Looking now on the internet it seems both types of flags would have been used at the different times.