After 1850 what was the biggest states' rights and secession?

After 1850, the biggest states' rights and secession issue revolved around the debate over slavery and its expansion into new territories. The Kansas-Nebraska Act of 1854, which allowed territories to decide for themselves whether to allow slavery, heightened tensions between pro-slavery and anti-slavery factions. This culminated in the secession of Southern states from the Union following the election of Abraham Lincoln in 1860, as they believed their rights to maintain the institution of slavery were under threat. Ultimately, these events led to the outbreak of the Civil War in 1861.