Indians

http://en.wikipedia.org/wiki/Native_Americans_in_the_American_Civil_War

When I was a kid I used to read comic books all the time.  Mostly they were war, historical or science fiction.  One of the things they would do is make the characters look like a particular group that they represented.  For example, a World War Two American Army squad might include one or more American Indians.  So to show who the Indian was, they would give him a weapon or article of clothing that would be typical of that ethnic group as part of his uniform.

 

Of course, most American Indians would dress just like white Americans if they participated directly in the war because everyone wore a uniform.  In the stress of combat over a prolonged period, it is not unusual to find troops have customized their uniforms to suit either their needs or their desires.  I have done this a few times and I intend to do it more.

 

For the American Civil War you could take some ACW soldiers and do a few head swaps and weapons exchanges on the soldiers with Native Americans to give some Indian flavor to a regular ACW unit. I have done this for WWII figures in 1/72nd scale.  Actually, I took American Indian figures and made them into WWII US Army troops by giving one an M-1 rifle to go with his full Indian attire.  Certainly doing a few head swaps would work well too, for several eras.  Native Americans fought in all American wars and have a proud heritage of service.