Like Men of War

This is a book that focuses more on the military service itself (as it acknowledges) and less on the broader picture than I would have preferred. In that way it can be a little slow because a lot of the military service that black troops performed was fatigue duty. Fatigue duty may not be as interesting as other responsibilities, either for the troops themselves at the time or for you to read about, but it's necessary to have a functioning military. The truth is that the United States won the Civil War when it did because black men served in the military and slaves fled to Union lines and assisted their armies, and refused to help the Confederate war effort. The confederate economy needed its slaves to survive and it died when enough of those slaves both refused to help and helped their enemies. The best articulation of this dynamic came from W.E.B. Du Bois in chapters 4 and 5 of Black Reconstruction.

If you want to know the particulars of what specific black regiments were doing during the war, this is a very interesting, detailed read, and perhaps the extensive bibliography will point you in other directions that will be fun to follow.