What legislation allowed settlers to vote on whether their state would be free or slave?

The Kansas-Nebraska Act is indeed the correct answer because it was the legislation that introduced the concept of popular sovereignty, allowing the settlers of a territory to decide for themselves whether they would allow slavery within their borders. Passed in 1854, the act led to the creation of the Kansas and Nebraska territories and effectively repealed the Missouri Compromise, which had previously prohibited slavery in certain northern territories.

By implementing this policy, the Kansas-Nebraska Act created significant tension between pro-slavery and anti-slavery factions, leading to violent conflicts known as "Bleeding Kansas." This directly illustrated the deep divisions within the country regarding the issue of slavery as states were allowed to make their own choices based on the will of the settlers.

The other options focus on different aspects of the national conversation surrounding slavery. The Missouri Compromise established a line dividing free and slave territories but did not allow individual states or territories to decide for themselves. The Compromise of 1850 involved various measures intended to address the status of territories acquired from the Mexican-American War but did not specifically grant the right to vote on slavery directly within individual territories as the Kansas-Nebraska Act did. The Dred Scott Decision was a Supreme Court ruling that articulated the legal status of enslaved