Uncle Tom's Cabin, written by Harriet Beecher Stowe and published in 1852, had a profound impact on the attitudes of Northerners regarding slavery. The correct answer would be:
3. They began to view it as a moral problem.
The novel depicted the harsh realities and inhumanity of slavery, effectively appealing to the emotions of its readers. It helped to shift public opinion in the North, making many people see slavery not just as a political or economic issue, but as a serious moral dilemma. This shift contributed to the growing abolitionist movement and increased tensions between the North and South leading up to the Civil War.