In 1850, most Northerners would never have dreamed they would be fighting a war against the South. Why did Northern public opinion change

The correct answer for this question is this one: " In 1850, most Northerners would never have dreamed they would be fighting a war against the South. The reason behind this is that t hey wanted to stay a complete country basically. The south wanted to break off because they believed in more slave labor while the north was based more on factories."