There are many events from the antebellum period that did this. The one that did it most dramatically was John Brown's raid on Harper's Ferry, VA and the northern reaction to that raid.
In this raid, Brown intended to use weapons from the armory to ignite a slave rebellion. If he had succeeded, his actions would clearly have led to the deaths of many Southerners. Many Northerners approved of his actions and saw him as a martyr. This indicated to Southerners that the North hated its way of life so much that Northerners were willing to praise someone who was trying to cause the deaths of many in the South.