The most accurate answer to why southern states seceded from the Union is:
B: They believed the union no longer represented their interests.
Southern states seceded primarily due to issues surrounding states' rights, the institution of slavery, and political power. They felt that the federal government and the growing power of the Northern states were infringing upon their rights and interests, particularly concerning slavery and economic regulations. While the other options may contain some elements related to the context of the time, option B best captures the primary motivation behind secession.