Which act significantly contributed to tensions leading to the Civil War?

The Fugitive Slave Act significantly contributed to the tensions leading to the Civil War because it mandated that enslaved individuals who escaped to free states be returned to their enslavers, and it imposed penalties on anyone who aided in their escape. This act heightened tensions between the North and South, as many in the North were morally opposed to slavery and found the enforcement of the Fugitive Slave Act to be a violation of their principles. It also led to increased hostility and conflict, as Northern states sought to undermine the law and protect escaped slaves, while Southern states demanded stricter enforcement.

The act fueled abolitionist sentiments in the North and further polarized the nation over the issue of slavery, contributing to the atmosphere of distrust and animosity that ultimately erupted into the Civil War. The other listed acts, while also important in their own right, did not have the same immediate and direct impact on the relationship between the Northern and Southern states regarding the institution of slavery.