"Shenandoah" with James Stewart

I've always enjoyed this movie, but after seeing it recently there are some things I have to question. First, how did the Anderson family get their hands on Henry repeating rifles? Second, how did the Anderson farm in the Shenandoah Valley, the epicenter of the fighting of the Civil War, escape relatively unscathed? The movie supposedly took place in 1864; Virginia during that period was pretty much starving to death. Third, why did the Union Army not retaliate against the Andersons for burning the POW train? Also, when Boy was captured by the (integrated)Union soldiers, they told Gabriel he was free. Usually the Union Army would take "contraband" and put them to work for the war effort, not simply say "you're free to go." Lastly, black soldiers did not fight alongside white soldiers as depicted in the battle scene where Gabriel rescues Boy.