2.which type of change—political, social, or economic—faced the most challenges? why were southerners against this type of change?

Because you didn't give much background information. I'd assumed that you are asking about the American Civil War began on 12nd April, 1861.

The social change faced the most challenge.The primary catalyst for secession was slavery, especially Southern anger at the attempts by Northern antislavery political forces to block the expansion of slavery into the western territories. Another explanation for secession, and the subsequent formation of the Confederacy, was Southern nationalism.