Which proposal aimed to address the issue of slavery in territories, leading to controversy and splits within political parties?

The Kansas-Nebraska Act, enacted in 1854, was a significant piece of legislation that aimed to address the issue of slavery in the newly organized territories of Kansas and Nebraska. This act was critical in shaping the political landscape of the United States during the height of sectional tensions.

One of the key features of the Kansas-Nebraska Act was its introduction of the concepts of "popular sovereignty," which allowed the settlers of these territories to decide for themselves whether they would permit slavery. This created considerable controversy as it effectively repealed the Missouri Compromise of 1820, which had previously prohibited slavery in the northern part of the Louisiana Purchase.

The Act ignited a fierce debate and spurred a violent struggle known as "Bleeding Kansas," where pro-slavery and anti-slavery factions clashed as they sought to influence the area's status on slavery. As a result, the Kansas-Nebraska Act contributed to significant splits within political parties, particularly leading to the collapse of the Whig Party and the rise of the Republican Party, which opposed the expansion of slavery.

This context illustrates how the Kansas-Nebraska Act was pivotal in addressing the contentious issue of slavery and the deepening divisions it created within the American political system during this period.