Short answers, pulled from the story.
In Texas v. White, decided on the 15th of April 1869, Chief Justice Salmon P. Chase ruled that unilateral secession is unconstitutional and that Texas had always remained part of an indestructible Union. The Court held that a state could only cease to be part of the union through revolution or through the consent of the states.
Eleven states seceded to form the Confederate States of America: South Carolina (the 20th of December 1860), Mississippi (the 9th of January 1861), Florida (the 10th of January 1861), Alabama (the 11th of January 1861), Georgia (the 19th of January 1861), Louisiana (the 26th of January 1861), Texas (the 1st of February 1861), Virginia (the 17th of April 1861), Arkansas (the 6th of May 1861), North Carolina (the 20th of May 1861), and Tennessee (the 8th of June 1861).
The Hartford Convention convened on the 15th of December 1814, and was attended by twenty-six New England Federalist delegates who opposed the War of 1812 and the dominance of the Virginia dynasty in the federal government. While the press called for secession and a separate peace with Britain, most delegates pursued a moderate course, recommending constitutional amendments instead. The convention became associated with disloyalty and hastened the decline of the Federalist Party.
While serving as Vice President in 1799, Thomas Jefferson secretly wrote the Kentucky Resolutions and stated in a private letter that he would rather sever from the Union than give up the rights of self-government. His biographer Dumas Malone argued that, had his actions become known at the time, Jefferson might have been impeached for treason.
Kentucky separated from Virginia and was admitted as a new state in 1792, Maine separated from Massachusetts in 1820, and West Virginia separated from Virginia in 1863 after anti-secessionist Virginians formed a government recognized by the United States.
A September 2017 Zogby International poll found 68 percent of Americans were open to states seceding. A 2021 poll found 52 percent of Trump voters and 41 percent of Biden voters supported partitioning the country along party lines. Polls from 2024 to 2026 found that support for state independence rose sharply in nine states, with 60 percent of Texans and 50 percent of Louisianans favoring peaceful independence.