The sectional conflict leading to the American Civil War was influenced by various events and ideologies in the 19th century. One pivotal development was the Kansas-Nebraska Act of 1854, which implemented the principle of popular sovereignty. This act set the stage for confrontation between pro-slavery and anti-slavery factions in the territories. Additionally, the growing visibility of abolitionist sentiments, the Dred Scott decision, and the implications of the Fugitive Slave Act further exacerbated tensions. Understanding these events is crucial in analyzing the broader causes of the Civil War. With these historical contexts in mind, which of the following developments most directly contributed to the polarization over the issue of slavery in the years leading to the Civil War?