Which act established Kansas and Nebraska as states and allowed their settlers to decide on slavery through popular sovereignty?

The Kansas-Nebraska Act is the piece of legislation that established the territories of Kansas and Nebraska and introduced the concept of popular sovereignty, which allowed the settlers of these territories to determine whether they would allow slavery. This act was passed in 1854 and effectively repealed the Missouri Compromise, which had previously prohibited slavery in those territories. By enabling settlers to vote on the issue of slavery, the Kansas-Nebraska Act was significant in exacerbating tensions between pro-slavery and anti-slavery factions, leading to heightened conflicts known as "Bleeding Kansas." This historical context illustrates the importance of the act in the broader narrative of the sectional conflict that contributed to the Civil War.