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 Advocates for secession are called disunionists by their contemporaries in various historical documents.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 to form the Confederate States of America, a procedure and body that the government of the United States refused to accept. The movement collapsed in 1865 with the defeat of Confederate forces by Union armies in the American Civil War.
In the history of the United States, the only territories to have been withdrawn from the country are the small portions of the Louisiana Purchase north of the 49th parallel north, established as the U.S.–British (now Canadian) border by the Treaty of 1818; and the territory of the Commonwealth of the Philippines, which became independent after the Treaty of Manila. The former is today part of Canada, while the latter corresponds to the Republic of the Philippines.
Boundaries of U.S. territories, such as the Nebraska Territory, were not defined precisely. The boundaries of each new state are set in the document admitting the former territory to the Union as a state, which Congress must approve. There are only two instances in U.S. history in which a portion of a state successfully seceded to create a new state: West Virginia, which separated from Virginia in 1863 and Maine separating from Massachusetts in 1820.
American Revolution
The Declaration of Independence states:
Historian Pauline Maier argues that this narrative asserted "the right of revolution, which was, after all, the right Americans were exercising in 1776"; and notes that Thomas Jefferson's language incorporated ideas explained at length by a long list of 17th-century writers, including John Milton, Algernon Sidney, John Locke, and other English and Scottish commentators, all of whom had contributed to the development of the Whig tradition in 18th-century Britain.
The right of revolution expressed in the Declaration was immediately followed with the observation that long-practiced injustice is tolerated until sustained assaults on the rights of the entire people have accumulated enough force to oppress them; then they may defend themselves. This reasoning was not original to the Declaration, but can be found in many prior political writings: Locke's Two Treatises of Government (1690); the Fairfax Resolves of 1774; Jefferson's own Summary View of the Rights of British America; the first Constitution of Virginia, which was enacted five days prior to the Declaration; and Thomas Paine's Common Sense (1776):
Gordon S. Wood quotes President John Adams: "Only repeated, multiplied oppressions placing it beyond all doubt that their rulers had formed settled plans to deprive them of their liberties, could warrant the concerted resistance of the people against their government".
Pre-Civil War political and legal views on secession
Overview
With origins in the question of states' rights, the issue of secession was argued in many forums and advocated from time to time in both the North and South in the decades after adopting the Constitution and before the American Civil War. Historian Maury Klein described the contemporary debate: "Was the Republic a unified nation in which the individual states had merged their sovereign rights and identities forever, or was it a federation of sovereign states joined together for specific purposes from which they could withdraw at any time?" He observed that "the case can be made that no result of the [American Civil] war was more important than the destruction, once and for all...of the idea of secession".