Which of the following factors best explains the territorial expansion of slavery in the middle of the nineteenth century?

Slavery in the Western Territories

To many nineteenth-century Americans, the expansion of slavery into western territories caused a great deal of controversy. Since the drafting of the Constitution in 1787, the North and the South had grown further apart in terms of economy, ideology, and society. The North, especially, was afraid that the South would force its “peculiar institution” upon the entire Union. These fears were realized when the expansion of slavery into western territories entered Congressional debates. The federal government, hoping to prevent a civil war, temporarily resolved the issue with compromises. As the compromises appeared to become more one-sided, however, sectional divides between the North and South became more pronounced.

• Watch Edward L. Ayers on the Civil War from The Gilder Lehrman Institute

The Sectional Divide between the North and the South

While the South utilized slavery to sustain its culture and grow cotton on plantations, the North prospered during the Industrial Revolution. Northern cities, the center of industry in the United States, became major metropolises due to an influx of immigrants. With this willing and cheap workforce, the North did not require a slave system. Although some northerners found the institution of slavery morally reprehensible, most did not believe in complete racial equality either. Slavery became even more divisive when it threatened to expand westward because non-slaveholding white settlers did not want to compete with slaveholders in the new territories.

First Steps Towards Controlling Slavery and Westward Expansion

Politicians were forced to deal with the issue of slavery and its westward expansion as early as the Missouri Compromise of 1820. The States had previously maintained a shaky balance in the Senate with an equal number of representatives from both Slave and Free States. As Missouri prepared to enter the Union as a Slave State, this tentative balance threatened to come undone. Henry Clay of Kentucky temporarily solved the issue by crafting the Missouri Compromise, bringing Missouri into the Union as a Slave State and, as a balance, Maine entered as a Free State. The Compromise also made future bondage illegal in all areas of the Louisiana Purchase north of the 36°30′ parallel with the exception of Missouri; all future states below this line would become Slave States.  This Compromise solved the immediate problem of slavery in the Louisiana Purchase by sweeping the real issue of slavery under the rug in order to placate both northern and southern politicians. In the years to come, politicians of both northern and southern states would not be so quick so compromise.

Conquests from Mexico

When the United States entered into a war with Mexico over Texas and its western territories, the issue of extending slavery in the west resurfaced in Congress. Representative David Wilmot of Pennsylvania first introduced a potential solution to the problem in 1846. His proposed amendment stated:

“…the acquisition of any territory from the Republic of Mexico by the United States, by virtue of any treaty which may be negotiated between them, and to the use by the Executive of the moneys herein appropriated, neither slavery nor involuntary servitude shall ever exist in any part of said territory, except for crime, whereof the party shall first be duly convicted.”

Wilmot’s proviso suggested that slavery should be prohibited in any territories acquired from Mexico. This would encourage white farmers to move west and implied that slavery was not an institution that should stretch far beyond its borders. Fearful of the southern “Slave Power” in Congress, many northern politicians quickly backed Wilmot’s amendment. Meanwhile, southern politicians railed that such an act was unconstitutional and vehemently blocked the passage of the Wilmot Proviso.  As a result, it never passed and the issue of slavery in westward territories remained a topic of heated debate.

Territories Becoming States

Congress was forced to revisit this issue yet again when California petitioned for statehood in 1849. Because California appeared to have anti-slavery inclinations, southern democrats were reluctant to let it enter the Union and disrupt the sectional balance in Congress. The resulting Compromise of 1850 was supposed to ensure that the interests of both sides remained intact. For the North, the Compromise guaranteed that California would enter the Union as a Free State and the slave trade would end in the District of Columbia. For the South, the Compromise promised that popular sovereignty would decide the question of slavery in the Utah and New Mexico territories. Furthermore, the Compromise reshaped the existing Fugitive Slave Act and required northerners to help capture runaway slaves.  This Act enraged the people of the North as it was a direct violation of their state laws and many argued that the “people of the free states are made [plantation owners’] constables and slave-catchers, bound as ‘good citizens’ to engage in a business at which their humanity must revolt…”

Kansas-Nebraska Act

Just four years later in 1854, new statehood controversies arose and forced the issue of slavery back into Congress. Kansas and Nebraska were both large territories petitioning for statehood. However, southerners opposed their admittance because the Missouri Compromise mandated that these two territories would enter as Free states. To satisfy southern states already threatening session, Congress passed the Kansas-Nebraska Act.  This new act repealed the Missouri Compromise; instead, the people living in Kansas and Nebraska would vote to determine the fate of the states.  When voters from nearby Missouri snuck into Kansas in order to vote to make the territory a slave state, tensions between the two sides exploded. War broke out in Kansas between pro-slavery sympathizers and abolitionists, earning it the nickname “bleeding Kansas.”  The violence in the west would soon spread east.

Check out this clip which highlights the escalating violence between the north and south on the issue of westward expansion:

The Beginnings of the Civil War

The fighting in Kansas foreshadowed the great fighting that would take place just six years later. The compromises of the early nineteenth century did not settle the issue of slavery and westward expansion. Instead, they suppressed the issue and acted as temporary salves. However, as the compromises appeared to benefit Slave States more often than they did Free States, sectional antagonisms between the North and the South were becoming more distinct. Ultimately, negotiations unraveled and a bloody Civil War erupted.

• Listen to James Oakes: Emancipation and the Question of Agency from The Gilder Lehrman Institute

This article helps answer “What role did western expansion play in the Civil War?” Themes: causes of the Civil War, the Civil War and Western Expansion, slavery, slavery and western expansion, Wilmot’s Proviso, Antebellum America, Bleeding Kansas, Civil War, Western Expansion, The West, the American West, African American history, economic history

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