Through 1920-1929, what roles did women and African Americans play in the military and how were African American troops treated?
During the time you mention, there were only women in the military in positions of "assistants" from what I can recall. Previously -- up through the civil war -- women had cheated and enlisted or had followed the men from battle to battle as camp followers but I do not recall that occurring after WWI.
Women were hired as office assistants and other similar things, but they were not actual members of the military at the time. During WWI and even more in WWII we saw women enlisting in WAC's and WAVES to help the war effort.
African Americans in the military were kept separate from the whites. They were enlisted and worked -- often in the dirtiest and worst jobs -- and were required to have white officers up to a certain point in time.
For a better feel for this, try searching for "Port Chicago" on the 'net and seeing what occurred there during WWII. You can only imagine that during WWI things were even worse. Few were involved in combat; most were involved in supporting roles.
As far as I am aware, there was no role for women in the military until WWII. The official army timeline for women in the Army does not start until then.
African-Americans, on the other hand, were part of the armed forces. Their numbers in the Army were relatively large at the beginning of the 1920s because of the large number of soldiers that had been needed for WWI. During the 1920s, however, the size of the Army was drastically reduced overall, and only blacks who had been in service before WWI were retained.