Final answer:
The Confederate soldiers under Major General Nathan Bedford Forrest's command at Fort Pillow fought ferociously, largely to discourage African American soldiers from joining the Union army, revealing strong racial prejudice and strategic motives.
Step-by-step explanation:
The Confederate soldiers under the command of Major General Nathan Bedford Forrest fought ferociously at Fort Pillow, leading to a tragic massacre of Union troops, particularly African American soldiers. This was not just an act of war but was also motivated by racial prejudice. Notably, the Fort Pillow Massacre became a symbol of the hatred that was part of the Civil War, as black Union soldiers were executed after their surrender, which contravened the norms of warfare. The primary motivation appears to be to discourage African American participation in the Union army and thus can be viewed as an act driven by a combination of racial hostility and war strategy intended to instill fear.
Considering the context in which this atrocity occurred, option D) 'They wanted to send a message and discourage African American soldiers from joining the Union army' aligns with the historical evidence and the motivations that were likely behind the actions of Forrest's troops at Fort Pillow.