In the anthology Four Hundred Souls, the chapter on Frederick Douglass emphasizes Douglass's view that the Civil War would change both the South and the North, as the North was still full of racist beliefs. Let's look at this in more detail.
Notice how the Northern states may have abolished slavery but still limited Black people in their rights. Abolition appealed only to some people in the North, certainly not to all. In fact, as the chapter explains, abolitionists were often opposed even with violence. Racism was indeed rampant in the North.
Look, too, at the discussion of Black soldiers in the Civil War and the reaction to them among Northerners. These men fought for their country, but they were not respected. In fact, they faced segregation, prejudice, and sometimes downright hatred. Douglass himself was confronted by mobs in the North.
The country, including the North, was a long way from racial equality, Douglass realized. There was still too much hatred as well as a disdain for abolition, which some people viewed as a tool to win the war rather than as a way to aid Black people. Be sure to take a look at some of the quotations from Douglass provided in the chapter, too. He speaks, for instance, of the opposition to Black political participation even within the Republican party.