Answer: B. Recruiting African Americans to fight against the Confederacy.
Explanation: African Americans like Frederick Douglass and Sojourner Truth played a crucial role in the Union's victory during the Civil War by advocating for the recruitment of African American soldiers to fight against the Confederacy. They argued that allowing African Americans to fight in the Union Army would not only help to secure victory for the Union, but also would provide an opportunity for African Americans to demonstrate their loyalty and worthiness as citizens. The recruitment of African American soldiers was initially met with resistance, but eventually, over 180,000 African Americans served in the Union Army and played a significant role in the Union's victory.