What did southern states due to protect slavery

The South did a lot to defend its right to maintain slavery. They continuously pressured the north and the Union to leave more liberty to the states, which effectively meant allowing the states to decide if they want to have slavery. They forced through a number of laws, such as the Second Amendment,  which allowed militias to defend the states, but in the South the Militias were slave patrols, so this among others, led to a protection of slavers in the South.