All of the fear of attacks and lack of protection is clearly outlined in the secession documents as well as the abuses of the constitution. These lead to secession. Secession removed all of the slavery questions, fears and constitutional abuses simply because the seceding states became a new nation with the responsibility of dealing with such problems should they arise. The United States no longer had to bother with the question of slavery or the expansion of slavery into the territories -- for them the question of slavery was answered. They only had to deal with the slave holding states which remained in the Union.
Lincoln's attack on Sumter solved the problem of what to do with the remained in the Union.
The war was fought over the right of the United States to occupy land in a sovereign nation and the right to impose the will of the United States will on that nation. If the South had freed all of the slaves in March 1861 and Anderson remained in Sumter, would the war have been avoided???