Answer: B. Some northerners did not want to fight a war to free slaves
Explanation:
President Lincoln was worried about making the Civil War about freeing enslaved people because he worried that some Northerners did not care about the issue enough to want to risk their lives for it.
This was the reason he waited so long to issue the Emancipation Proclamation but when he eventually did and the nation saw the bravery of the African Americans that joined the Civil War, opposition to the War being about slavery gradually dissipated.