Why did some northerners want to recruit african americans into the union army?

Northerners wanted Lincoln to free the slaves and, thereby, allow them to join the Union army.Some signed up as Union soldiers, while other free African Americans formed their own units and fought for the Union.In what ways did African American soldiers face more difficulties than white soldiers did?
Some white Union soldiers did not want the African Americans to fight with them. African American soldiers were paid less than white soldiers. And African American soldiers who were captured by the South were often executed or sold into slave labor. In total , it was to have more man power & beat the confederates .