What was the major issue between the north and the south in the 1850s?

The major issue between the North and the South in the 1850s was slavery, particularly its expansion into newly acquired territories and states. The North, increasingly industrialized and anti-slavery, opposed the spread of slavery, while the agrarian South relied on slave labor for its economy and sought to protect and expand the institution. This tension led to significant political conflict, including the Kansas-Nebraska Act and the Dred Scott decision, ultimately contributing to the outbreak of the Civil War.