Claim: The restrictions on the expansion of slavery in the United States evolved significantly between 1780 and 1860, reflecting the shifting political and social landscape of the nation.

Early Restrictions (1780s-1820s):
In the early years following the American Revolution, some Northern states began implementing gradual emancipation laws, which aimed to abolish slavery over time. For example, Pennsylvania passed a gradual emancipation law in 1780, followed by other Northern states like Massachusetts and New York. These laws did not immediately end slavery but set a precedent for restricting its expansion.

Additionally, the Northwest Ordinance of 1787 prohibited slavery in the territories northwest of the Ohio River, establishing a region where slavery would not be permitted. This marked a significant restriction on the expansion of slavery into newly acquired territories.

Missouri Compromise (1820):
The Missouri Compromise of 1820 marked a pivotal moment in the debate over slavery expansion. With the admission of Missouri as a slave state and Maine as a free state, the compromise maintained a balance between free and slave states in the Union. Furthermore, it established a line across the Louisiana Territory, with slavery prohibited north of the line (except for Missouri) and allowed south of it. While it temporarily eased tensions, it also showcased the deepening divide between Northern and Southern states over the issue of slavery expansion.

Compromise of 1850 and Fugitive Slave Act:
The Compromise of 1850 attempted to address the issue of slavery in newly acquired territories from the Mexican-American War. It admitted California as a free state but also included the controversial Fugitive Slave Act, which required Northern states to assist in the capture and return of escaped slaves. This act intensified opposition to slavery expansion in the North, as it forced citizens to participate in the institution of slavery, leading to further tensions between North and South.

Kansas-Nebraska Act (1854):
The Kansas-Nebraska Act of 1854 repealed the Missouri Compromise line and allowed the territories of Kansas and Nebraska to decide on the issue of slavery through popular sovereignty. This led to violent conflicts between pro-slavery and anti-slavery settlers in Kansas, earning it the moniker "Bleeding Kansas." The Act's repeal of the Missouri Compromise inflamed tensions and showcased the increasingly radical positions on both sides of the slavery debate.

Dred Scott Decision (1857):
The Supreme Court's ruling in the Dred Scott case further complicated the issue of slavery expansion. The decision not only declared that Congress could not prohibit slavery in the territories but also asserted that African Americans, whether free or enslaved, were not U.S. citizens and did not have rights to sue in court. This decision nullified the restrictions placed on slavery expansion by previous legislation and emboldened proponents of slavery.