Final answer:
Southern states seceded from the Union because they believed the federal government was infringing on their states' rights, particularly the right to own slaves and uphold white supremacy, leading to their belief in the need for self-government separate from northern influence.
Step-by-step explanation:
The feeling among Southerners that they were fighting for the right to self-government is best explained by their belief that the federal government was overreaching its powers and not adequately representing Southern interests. Southern states felt their autonomy was being infringed upon, especially regarding their right to own property (slaves) and their ability to take that property anywhere in the country. This issue, along with the desire to preserve what they saw as the principles of the American Revolution and protect states' rights, was central to the secessionist movement.
Secessionists like Jefferson Davis argued that they were defending the liberty fought for by their ancestors, and used the concept of white supremacy to garner support from non-slaveholders. Influential documents like the Mississippi declaration of secession clarified that slavery was at the core of their concerns. They believed that the newly-elected President Lincoln and Northern interests, which were seen as anti-slavery, would undermine their way of life, prompting their secession from the Union.