The origins of the American Civil War lay in the outcome of another war fought by Americans fifteen years earlier: the Mexican War. The peace treaty signed with Mexico in 1848 transferred 700,000 square miles of Mexican territory to the United States. Many Southerners wanted to introduce slavery into at least part of this new territory; antislavery Northerners wanted to keep it out. From 1848 to 1861 this issue dominated American politics. The Compromise of 1850 attempted to resolve all questions relating to slavery by admitting California as a free state, leaving it up to the residents of New Mexico and Utah territories whether they wanted slavery, abolishing the slave trade in Washington, D.C. but guaranteeing slavery itself there, and passing a strong fugitive slave law giving the national government power to return escaped slaves to their owners in the South.

The origins of the American Civil War lay in the outcome of another war fought by Americans fifteen years earlier: the Mexican War. The peace treaty signed with Mexico in 1848 transferred 700,000 square miles of Mexican territory to the United States. Many Southerners wanted to introduce slavery into at least part of this new territory; antislavery Northerners wanted to keep it out. From 1848 to 1861 this issue dominated American politics. The Compromise of 1850 attempted to resolve all questions relating to slavery by admitting California as a free state, leaving it up to the residents of New Mexico and Utah territories whether they wanted slavery, abolishing the slave trade in Washington, D.C. but guaranteeing slavery itself there, and passing a strong fugitive slave law giving the national government power to return escaped slaves to their owners in the South.

This compromise only papered over the controversy. It burst forth again in 1854, when Southerners in Congress demanded the repeal of the ban on slavery in territories north of the latitude 36* 30’ by the Missouri Compromise of 1820 as the price for passage of the Kansas-Nebraska Act organizing these territories. Three years later the Southern-dominated Supreme Court ruled in the Dred Scott case that Congress had no power to ban slavery from any territory. A new antislavery Republican party sprang up and gained a majority in the North for its platform to reverse this law and ruling. This issue infused the debates between Abraham Lincoln and Stephen A. Douglas in the Illinois senatorial contest of 1858, won by Douglas, and the presidential election of 1860, won by Lincoln. With the latter election the storm broke, precipitating seven Southern states out of the Union.

A satire on President Zachary Taylor’s attempts to balance Southern and Northern interests on the question of slavery in 1850. Source: Library of Congress, Prints & Photographs Division, LC-USZC4-4552