In the history of the United States, a slave state was a U.S. state in which the practice of slavery was legal, and a free state was one in which slavery was prohibited or being legally phased out. Historically, in the 17th century, slavery was established in a number of English overseas possessions. In the 18th century, it existed in all the British colonies of North America. In the Thirteen Colonies, the distinction between slave and free states began during the American Revolutionary War (1775–1783). Slavery became a divisive issue and was the primary cause of the American Civil War. The Thirteenth Amendment to the United States Constitution, ratified in 1865, abolished slavery throughout the United States, and the distinction between free and slave states ended.
In the 1770s, blacks throughout New England began sending petitions to northern legislatures demanding freedom. Five of the Northern self-declared states adopted policies to at least gradually abolish slavery: Pennsylvania (1780), New Hampshire and Massachusetts (1783), Connecticut and Rhode Island (1784). Vermont had abolished slavery in 1777, while it was still independent, and when it joined the United States as the 14th state in 1791, it was the first state to join untainted by slavery. These state jurisdictions thus enacted the first abolition laws in the Americas.
In the south, Kentucky was created a slave state from Virginia (1792), and Tennessee was created a slave state from North Carolina (1796). By 1804, before the creation of new states from the federal western territories, the number of slave and free states was eight each. In popular usage, the geographic divide between the slave and free states was called the Mason-Dixon line (between Maryland and Pennsylvania or Delaware).
The 1787, United States Constitutional Convention debated slavery, and for a time slavery was a major impediment to passage of the new constitution. As a compromise, the institution was acknowledged though never mentioned directly in the constitution, as in the case of the Fugitive Slave Clause. In 1808, the United States outlawed the international slave import trade, but the domestic trade in half the states continued.
During the War of 1812, the British accepted as free all slaves who came into their hands, with no conditions as to military service such as had been made in Dunmore's Proclamation in the Revolutionary War. By the end of the War of 1812, the momentum for antislavery reform, state by state, appeared to run out of steam, with half of the states having already abolished slavery (Northeast), prohibited from the start (Midwest) or committed to eliminating slavery, and half committed to continuing the institution indefinitely (South).
The potential for political conflict over slavery at a federal level made politicians concerned about the balance of power in the United States Senate, where each State was represented by two Senators. With an equal number of slave states and free states, the Senate was equally divided on issues important to the South. As the population of the free states began to outstrip the population of the slave states, leading to control of the House of Representatives by free states, the Senate became the preoccupation of slave-state politicians interested in maintaining a Congressional veto over federal policy in regard to slavery and other issues important to the South. As a result of this preoccupation, slave states and free states were often admitted into the Union in opposite pairs to maintain the existing Senate balance between slave and free states.
As part of the Compromise of 1850, California was admitted as a free state (1850), without a slave state pair. To avoid creating a free state majority in the Senate, California agreed to send one pro-slavery and one anti-slavery senator to Congress.
In 1854, the Missouri Compromise of 1820 was superseded by the Kansas–Nebraska Act, which allowed white male settlers in the new territories to determine through popular sovereignty whether they would allow slavery within each territory. The result was that pro- and anti-slavery elements flooded into Kansas with the goal of voting slavery up or down, leading to Bleeding Kansas.Nicole Etcheson. Bleeding Kansas: Contested Liberty in the Civil War Era (2006). ch 1. An effort was initiated to organize Kansas for admission as a slave state, paired with Minnesota, but the admission of Kansas as a slave state was blocked because of questions over the legitimacy of its slave state constitution. Anti-slavery settlers in "Bleeding Kansas" in the 1850s were called Free-Staters and Free-Soilers, because they fought (successfully) to include Kansas in the Union as a free state in 1861.
When the admission of Minnesota proceeded unimpeded in 1858, the balance in the Senate was lost; a loss that was compounded by the subsequent admission of Oregon as a free state in 1859.
After 1812, and until 1850, maintaining the balance of free and slave state votes in the Senate was considered of paramount importance if the Union were to be preserved, and states were typically admitted in pairs:
The balance was maintained until 1850:
The Civil War (1861-1865) disrupted and eventually ended slavery:
President Lincoln had issued the Emancipation Proclamation on January 1, 1863, which exempted from emancipation the border states (four slave states loyal to the Union) as well as some territories occupied by Union forces within Confederate states. Two additional counties were added to West Virginia in late 1863, Berkeley and Jefferson. The slaves in Berkeley were also under exemption but not those in Jefferson County. As of the census of 1860, the 49 exempted counties held some 6000 slaves over 21 years of age who would not have been emancipated, about 40% of the total slave population. The terms of the Willey Amendment only freed children, at birth or as they came of age, and prohibited the importation of slaves.
West Virginia became the 35th state on June 20, 1863, and the last slave state admitted to the Union.Alton Hornsby, Jr., Black America, A State-by-State Historical Encyclopedia, Greenwood, 2011, vol. 2, pg. 922 Eighteen months later, the West Virginia legislature completely abolished slavery, and also ratified the 13th Amendment on February 3, 1865.
The border states of Maryland (November 1864) and Missouri (January 1865),
one of the Confederate states, Tennessee (January 1865), and the new state of West Virginia (February 1865), abolished slavery just prior to the end of the Civil War (May 1865). In the District of Columbia, slavery was abolished in 1862.American Memory " Abolition in the District of Columbia", Today in History, Library of Congress, viewed December 15, 2014. On April 16, 1862, Lincoln signed a Congressional act abolishing slavery in the District of Columbia with compensation for slave owners, five months before the victory at Antietam led to the Emancipation Proclamation. However, slavery persisted in Delaware, Kentucky,