1790: Slave population in Federal Census: 698,000
1799: New York state enacts gradual abolition of slavery
1801: Gabriel Plot frightens whites in Virginia who believe there was plot for slave uprising
1804: New Jersey enacts gradual abolition of slavery, the final northern state to do so
1808: Congress outlaws the international slave trade. U.S. Navy and British Royal Navy enforce the prohibition. Some 250,000 slaves were smuggled in anyway before 1860. Some smugglers are caught and executed.
- Slave population in Census: 1,538,000
- Missouri Compromise admits Maine as a free state, and Missouri as slave state, but restricts anymore slavery north of 36° 30' line. Abrogated by Kansas Nebraska Act of 1854.
1822: Denmark Vesey frightens whites in South Carolina, who believe there was plot for slave uprising
1828: John C. Calhoun's South Carolina Exposition and Protest propounds nullification doctrine saying a state can nullify a federal law. Calhoun threatens secession over tariffs that aid new industries in North. In 1840, Calhoun states that "It is our duty to force the issue [of slavery] on the North. Had the South, or even my own State, backed me, I would have forced the issue on the North in 1835."  Calhoun also objected to the use of taxes and tariffs collected in one state being used for internal improvements to another state. []
1829: Black abolitionist David Walker issues Appeal to the Colored Citizens of the World calling on slaves to revolt; none revolt.
1830: Daniel Webster delivers a memorable Reply to Hayne on January 27, denouncing the notion that Americans must choose between liberty and union. "Liberty and Union, now and forever, one and inseparable!" he cries.
- Abolitionist William Lloyd Garrison begins publishing The Liberator and demands immediate emancipation because slavery is a personal sin.
- Nat Turner leads a real slave revolt in Southampton County, Virginia.
- Responding to new Christian sensibilities, the rising importance of slave labor in the Southern cotton economy, the Nat Turner uprising, and the rise of abolitionism, Southern defenders of slavery start seeing it not as a "necessary evil," but a "positive good."
1836: In response to the petition campaigns of the American Anti-Slavery Society, the U.S. House of Representatives adopts a gag rule, by which all antislavery petitions presented to the House would be immediately tabled, without discussion. John Quincy Adams leads an eight year battle against the gag rule, arguing that slavery, or the Slave Power, as a political interest, threatens constitutional rights.
1837: Mob of Irish and southern men kills abolitionist and anti-Catholic editor Elijah P. Lovejoy in Alton, Illinois;
1839: Slaves revolt on the Amistad; trial in federal court leads to release of rebels, who are returned to Africa.
1840: Slave population in Census: 2,487,000
1846: James D.B. DeBow establishes DeBow's Review, the leading Southern magazine warning against depending on the North economically. DeBow's Review emerges as the leading voice for secession. DeBow emphasizes the South's economic underdevelopment, relating it to the concentration of manufacturing, shipping, banking, and international trade in the North.
1851: Southern Unionists in several states defeat secession measures; Mississippi's convention denies the existence of the right to secession.
- George Fitzhugh's The Pro-Slavery Argument is published.
- Harriet Beecher Stowe publishes Uncle Tom's Cabin. A forceful indictment of slavery, the novel sells 500,000 copies and stiffens northern resistance to fugitive slave law. Whig Party is decisively defeated in the election and fades away, abandoned by leaders and voters.
- Democrat Stephen A. Douglas proposes the Kansas-Nebraska Bill to open good farmland to settlement (and help railroads).
- The Kansas Nebraska Act is passed, providing that popular sovereignty in the territories should decide "all questions pertaining to slavery." It effectively repeals the Missouri Compromise.
- In uproar against Kansas-Nebraska Act, new Republican party is formed with anti-slavery base across North. Includes many former Whigs and Free Soilers, and some Democrats. Sweeps fall elections in northern states. Abraham Lincoln emerges as Republican leader in West
- Know-Nothing party sweeps state and local elections in parts of North; demands ethnic purification, opposes Catholics (because of Pope), opposes corruption in local politics. The party has no real leaders and soon fades away.
- The Ostend Manifesto proposing to annex Cuba is denounced by the free-soil press as a conspiracy to extend slavery.
:1855-1856: Violence breaks out in "Bleeding Kansas"
- 1856: Preston Brooks canes Charles Sumner on floor of Senate; North takes the lesson that compromise is harder and violence is near surface. In presidential election Republican John C. Frémont crusades against slavery; the slogan is "Free speech, free press, free soil, free men, Frémont and victory!" Democrats countercrusade, warning of civil war, and win.
- Short economic depression in major cities; See Panic of 1857
- Walker Tariff of 1846 is lowered still more and is supported by both North and South; it reduces protection to northern industry.
- Southern opposition kills the Pacific Railway Bill of 1860 and homestead laws.
- Douglas breaks with President Buchanan over Kansas because Buchanan supported the undemocratic Southern position; bitter feud inside Democratic party.
- Proslavery Lecompton constitution defeated by popular referendum in Kansas in August.
- Lincoln and Douglas debate; Lincoln emerges as nationally known moderate spokesman for Republicans
- William Yancey advocates a Southern confederacy.
- James Hammond exclaims, "Cotton is King!", meaning Europe will intervene to protect source of vital raw material
- John Brown attempts to ignite slave rebellion in Virginia by attack on federal armory at Harper's Ferry; no rebellion; captured, tried for treason to state of Virginia, and hanged; becomes martyr to North; alarms South as exemplar of fanatical Yankee abolitionist trying to start bloody race war; Republican Party disavows Brown, who had financial support from Boston abolitionists.
- Slave population in Census: 3,954,000
- Southern "fire-eaters" oppose front runner Stephen A. Douglas' bid for the Democratic presidential nomination. The Democrats begin splitting North and South.
- Radicals William H. Seward of New York, Salmon P. Chase of Ohio, and Simon Cameron of Pennsylvania are leading contenders for the Republican presidential nomination, along with Lincoln. Illinois out-maneuvers other states and on May 16, Lincoln wins the Republican nomination at Chicago convention.
- The Morrill Tariff passes the House of Representatives on a strict sectional vote, supported by the north and opposed by the south; it does not pass Senate.
- The Democratic party splits. Main group supports Douglas. Southern Democrats support John C. Breckinridge.
- Former Whigs from the border states form the Constitutional Union Party, nominating John C. Bell for president on a one-issue platform of national unity.
- Four candidates as parties wage campaigns. Douglas and Lincoln compete for Northern votes. Bell, Douglas and Breckinridge compete for Southern votes.
- Abraham Lincoln wins the 1860 election.
- Secession: South Carolina convention declared on December 20 "that the Union now subsisting between South Carolina and other states under the name of the 'United States of America' is hereby dissolved"
- Process of secession begins.
- The six other states of the Deep South secede, and together with South Carolina form the Confederate States of America. They are not recognized by U.S. government, or any government. Border states refuse to join Confederacy.
- Last major N-S links broken as Presbyterian and Episcopal Churches split North and South
- Numerous compromise proposals are rejected; they all involve protection of slavery (none involve tariffs or economic deals); Confederacy demands complete independence and will not negotiate a return to the Union.
- Confederates capture US arsenals and forts in CSA states; General David E. Twiggs surrenders one-fourth of US Army in Texas, then joins Confederacy.
- Northern governors secretly buy arms and prepare regiments for war; CSA--apparently unaware--does not do this
- Virginia leaders negotiate with Lincoln: they will stay out of CSA but he must promise not to invade. No promise is made.
- Lee offered command of Union army; Lee says agrees unless his home state of Virginia joins the Confederacy.
- Buchanan decides to keep Fort Sumter in Charleston harbor
- CSA army fired on Fort Sumter; it surrenders.
- Northern uprising--mass meetings everywhere to demand Lincoln overthrow the rebellion.
- Lincoln calls every governor for troops (75,000) to recapture Fort Sumter, via invasion of Virginia and North Carolina.
- Pennsylvania, New York, Massachusetts send troops to Washington.
- Virginia, North Carolina, Tennessee and Arkansas reject Lincoln's order to provide troops for an invasion; they secede and join CSA.
- Kentucky refuses troops and declares neutrality. Lincoln seizes control of Missouri and Maryland; thousands of pro-CSA men under military arrest.