Stowe's Uncle Tom's Cabin widened the chasm between the North and the South, greatly strengthened Northern abolitionism, and weakened British sympathy for the Southern cause. The most influential novel ever written by an American, it was one of the contributing causes of the Civil War. While Stowe did not start the war, Uncle Tom's Cabin did increase the differences between the North and the South. Many Northerners realized how unjust slavery was for the first time. With increasing opposition to slavery, Southern slave owners worked even harder to defend the institution.