| •1842 | John C. Frémont leads expedition along the Oregon Trail |
| •1848 | Gold discovered in California |
| •1850 | Compromise of 1850 |
| Fugitive Slave Act |
| •1852 | Harriet Beecher Stowe publishes Uncle Tom's Cabin |
| •1854 | U.S.-Japanese treaty allows for mutual trading |
| Republican Party founded |
| Kansas-Nebraska Act |
| •1854–1858 | Period of violence in Bleeding Kansas |
| •1857 | Dred Scott case |
| •1858 | Lincoln-Douglas debates |
| •1859 | John Brown's raid on Harpers Ferry |
| •November 1860 | Abraham Lincoln elected president |
| •December 1860 | South Carolina secedes from the Union |
| •January 1861 | Mississippi, Florida, Alabama, Georgia, Louisiana, and Texas secede |
| •February 1861 | Confederate States of America established |
| •March 1861 | Lincoln inaugurated as president |