Secession in the United States
In the context of the United States, secession primarily refers to the voluntary withdrawal of one or more states from the Union that constitutes the United States; but may loosely refer to leaving a state or territory to form a separate territory or new state, or to the severing of an area from a city or county within a state. Advocates for secession are called disunionists by their contemporaries in various historical documents.
Threats and aspirations to secede from the United States, or arguments justifying secession, have been a feature of the country's politics almost since its birth. Some have argued for secession as a constitutional right and others as from a natural right of revolution. In Texas v. White (1869), the Supreme Court ruled unilateral secession unconstitutional, while commenting that revolution or consent of the states could lead to a successful secession.
The most serious attempt at secession was advanced in the years 1860 and 1861 as 11 Southern states each declared secession from the United States, and joined together to form the Confederate States of America. This movement collapsed in 1865 with the defeat of Confederate forces by Union armies in the American Civil War.