- Year: 1820

- Event Name and Summary: Missouri Compromise; admitted Missouri as a slave state and Maine as a free state, maintaining the balance of power in Congress.

- Region Benefitted: Temporarily benefitted both North and South by maintaining balance.

- This event was significant as it highlighted the growing tensions between free and slave states, setting the stage for future conflicts.

- Year: 1845

- Event Name and Summary: Manifest Destiny; the belief that the U.S. was destined to expand across the continent, promoted by President James K. Polk.

- Region Benefitted: Benefitted the South and West by promoting expansion.

- This ideology fueled expansionist policies that exacerbated sectional tensions over slavery in new territories.

- Year: 1846-1848

- Event Name and Summary: Mexican War; conflict between the U.S. and Mexico, resulting in the U.S. acquiring territories in the southwest.

- Region Benefitted: Benefitted the South by opening new lands for potential slave states.

- The acquisition of new territories intensified the debate over the extension of slavery, contributing to sectional discord.

- Year: 1820s-1860s

- Event Name and Summary: Growth of Sectionalism; increasing division between North and South over economic, social, and political issues.

- Region Benefitted: Benefitted neither region; increased tensions.

- : This growing divide was a critical factor in the eventual secession of Southern states.

- Year: 1850

- Event Name and Summary: Compromise of 1850; series of laws intended to settle the issue of slavery in territories acquired from Mexico.

- Region Benefitted: Temporarily benefitted both regions by delaying conflict.

- This compromise was a temporary solution that ultimately failed to address the root causes of sectional conflict.

- Year: 1850s

- Event Name and Summary: Popular Sovereignty; allowed territories to decide the issue of slavery by vote.

- Region Benefitted: Benefitted the South by potentially expanding slavery.

- This principle led to violent conflicts, such as "Bleeding Kansas," highlighting the deep divisions in the country.

- Year: 1854

- Event Name and Summary: Kansas-Nebraska Act; allowed territories to decide on slavery, nullifying the Missouri Compromise.

- Region Benefitted: Benefitted the South by opening new territories to slavery.

- This act led to increased tensions and violence, further polarizing the nation.

- Year: 1857

- Event Name and Summary: Dred Scott Decision; Supreme Court ruling that African Americans were not citizens and Congress could not ban slavery in territories.

- Region Benefitted: Benefitted the South by affirming the legality of slavery.

- This decision outraged the North and galvanized anti-slavery sentiment, pushing the nation closer to war.

- Year: 1859

- Event Name and Summary: John Brown’s Raid; an abolitionist-led attack on the federal armory at Harpers Ferry to incite a slave revolt.

- Region Benefitted: Benefitted neither region; increased tensions.

- This raid heightened fears of slave uprisings in the South and increased support for abolition in the North.

- Year: 1860

- Event Name and Summary: Election of Abraham Lincoln; Lincoln's election as president led to the secession of Southern states.

- Region Benefitted: Benefitted the North by electing an anti-slavery president.

Lincoln's election was the final catalyst for Southern secession, making war inevitable.

- Year: 1861

- Event Name and Summary: Attack on Fort Sumter; Confederate forces fired on the federal fort, marking the start of the Civil War.

- Region Benefitted: Benefitted neither region; initiated the Civil War.

- This event marked the official beginning of the Civil War, a conflict that would determine the fate of the Union and slavery in America.