Significant Antebellum Events

Annexation of Texas
Addition of Texas to the U.S. adds a major slave state to the Union
Wilmot Proviso
Though never passed by Congress, this proposal to ban slavery from territories taken from Mexico Keeps the slavery issue in Congressional view.
Treaty of Guadalupe Hidalgo
While ending the Mexican-American War, this also adds a huge section of the Southwest to the U.S. "Should these states be allowed to have slaves?" is a key question.
Compromise of 1850
While not satisfying either abolitionists or slavery advocates, this brings California in as a free state and strengthens the Fugitive Slave Law. It also allows Utah and New Mexico territory residents to decide on slavery.
Uncle Tom's Cabin
Publication of Harriet Beecher Stowe's novel takes the message of abolitionism to a broad audience. Over 300,000 copies are sold in the first year. It is also produced as a play throughout the world. Good, kindly blacks are portrayed as victims of a cruel system.
Kansas-Nebraska Act
Repealing the Missouri Compromise, the K-N Act gives residents the right to decide on the issue of slavery. Proposed by Stephen Douglas, this pushes many former Whigs into the new Republican Party, which opposes the extension of slavery beyond its current locations.
Bleeding Kansas
Violent clashes between pro- and anti-slavery advocates. 200 deaths result as settlers pour in to Kansas on both sides.
Dred Scott case
Critical ruling by the Supreme Court that slaves are not citizens and that Congress has no authority to ban slavery from the territories. Huge victory for pro-slavery forces.
Lecompton Constitution
Kansas pro-slavery constitution that is adopted after anti-slavery forces boycotted the state's constitutional convention but defeated it by 10,000 votes, clearly indicating an anti-slavery majority. Pres. Buchanan supports the Lecompton document, greatly distressing Republicans. Kansas voters reject it again and it isn't't until 1861 that Kansas joins the Union as a free state.
Lincoln-Douglas debates
In a race for an Illinois Senate seat, Douglas defends popular sovereignty and accuses the Republicans of favoring war and social equality of the races.  Lincoln opposes the extension of slavery into the territories, but does not advocate its abolition in the South. The debate makes Lincoln a national figure.
John Brown's Raid
While failing in his attempt to begin a slave uprising, John Brown helps define the line between abolitionists and those opposed to slavery, but unwilling to take a stand against it. Brown's action convinces some Southerners that nothing but withdrawal from the nation would preserve slavery in the South.
Election of 1860
While winning less than 40% of the popular vote, Lincoln achieves a victory in the electoral college over a divided Democratic Party.
Jefferson Davis sworn in as Confederate president
February 1861
Seven seceding states establish the Confederate States of America, claiming they are acting in the spirit of 1776.
Firing on Ft. Sumter
April 1861
 Lincoln sends supplies to the fort in Charleston harbor, knowing the South would attack. Several southern states secede and the conflict has become war.