The correct answer is increasing sectionalism.
During the early to mid 19th century, the American economy was developing in very different ways. For example, the Northern states were becoming more industrialized and focused significantly on the production of manufactured goods. On the other hand, Southern states still relied heavily on slave labor to grow cash crops (especially cotton). This was vastly different than the North, as slavery had been outlawed in many of these states.
The issue of slavery, it's existence, and its extension into new territories in the west caused significant problems between Northern and Southern states. This was especially true when Northern and Southern politicians meet in Congress to discuss these issues.