Hold the idea of a separation of these States, those that are free to form one government, and those that are slave-holding to form another, as such an impossibility. . . . There are natural causes that would keep and tie us together, and there are social and domestic relations which we could not break if we would, and which we should not if we could. –Daniel Webster,
1850

Based on Webster’s words, many southerners would have most likely concluded that

abolitionist forces from the North were about to invade.
northerners were going to leave the Union out of anger.
the possibility of compromise on the issue of slavery still existed.
the North was going to stop importing cotton from the South.