Free and slave states, 1821–1861
The Missouri Compromise, the Compromise of 1850, the Kansas–Nebraska Act and secession, on the borders of the day.
Blue is free; red and orange are where slavery was legal. Solid colors are states. Striped areas are territories, which Congress ran until they became states.
Every step in words
1820: The Missouri Compromise
Borders as of 10 August 1821, the day Missouri became a state
Missouri asked to join as a slave state, which would have tipped the Senate. The Missouri Compromise of 1820 let Missouri in with slavery and Maine in as a free state, leaving 12 free and 12 slave states. It also banned slavery in the rest of the Louisiana Purchase north of 36°30′ (the dashed line).
The deal kept the peace for 30 years, but it showed how dangerous the question of slavery in new lands had become. Thomas Jefferson called the crisis “a fire bell in the night.”
1850: The Compromise of 1850
Borders as of 13 December 1850
California joined as a free state, making 16 free and 15 slave states. Utah and New Mexico territories were set up without a ban on slavery; their settlers would decide. Texas gave up its claim to land in New Mexico. A tough new Fugitive Slave Act came with the deal.
The Fugitive Slave Act forced Northerners to help return people who had escaped slavery, which turned many of them against slavery. “Popular sovereignty” in the West would be tried again, with violent results, in Kansas.
1854: The Kansas–Nebraska Act
Borders as of 4 August 1854
Stephen Douglas's Kansas–Nebraska Act created Kansas and Nebraska territories and let their settlers decide about slavery. That threw out the Missouri Compromise's ban north of 36°30′, so the line is gone.
Pro- and antislavery settlers rushed into Kansas and fought (“Bleeding Kansas”). Anger at the act broke up the Whig Party and created the Republican Party, which was against slavery spreading west.
1861: Secession
Borders as of 8 June 1861
After Abraham Lincoln won the 1860 election, seven Deep South states left the Union and formed the Confederacy. After the attack on Fort Sumter in April 1861 and Lincoln's call for troops, four more left. Four slave states (Delaware, Maryland, Kentucky and Missouri) stayed in the Union.
Keeping the border states mattered so much to Lincoln that the Emancipation Proclamation (1863) did not free people enslaved there. Virginia's western counties refused to secede and became the state of West Virginia in 1863.
Where the borders come from
- Atlas of Historical County Boundaries: Historical States and Territories, 1783–2000, The Newberry Library. CC0 (public domain).
- Natural Earth coastlines, lakes and countries (1:50m), Natural Earth. Public domain.
- The 36°30′ line, as described in the Missouri Compromise act (3 Stat. 545, section 8), U.S. Congress, 1820. Public domain.
What to keep in mind
- Borders, and which places were states or territories on each date, come from the Atlas. Which states were free or slave, and the rules in each territory, come from the laws named in each step; the map's tables list them state by state.
- The 36°30′ line is drawn along that latitude from the Missouri–Arkansas border to the 1819 border with Spain, as the 1820 law describes it. Unorganized land and Indian Territory are split along it.
- On the 1861 step, Virginia still includes West Virginia, and the Confederacy's claim to the southern half of New Mexico Territory (made in August 1861) is not shown.
- Borders are from the Newberry Library's Atlas of Historical County Boundaries, which records every change to the day, with the law or treaty behind it. To keep the map quick to load, coastlines and borders are smoothed, so small bends and tiny islands are missing.