Sure, if you believe that history began with the Battle of Big Bethel, June 10, 1861, where the first Confederate soldier was killed directly in battle, then you might suppose that Civil War didn't begin until the Union invaded the Confederacy.
But in fact, Confederates began threatening and committing acts of military aggression against Union officials from the very week of their first declaration of secession, December 20, 1860 -- seizing forts around Charleston harbor and demanding Sumter's surrender.
So any claim that the Confederacy was not an existential threat against the United States is pure bunk.
Indeed, they went so far as to declare part of the Confederacy states and territories which refused, or had no legal right to declare their secession -- Missouri, Kentucky, Oklahoma, New Mexico.
And before war's end, the Confederacy had invaded or raided into every US state & territory it could reach, including: Maryland, Pennsylvania, Ohio, Indiana, Kentucky, Missouri, Kansas, Oklahoma & New Mexico territories, as well as minor insurgent attacks in California, Colorado and Vermont.
In every such invasion, Confederate forces took what they needed, sometimes "paying for", more often not, and always destroying anything reckoned as militarily valuable (i.e., railroad equipment & bridges).
That the Civil War was fought mostly in the South only reflects the Confederacy's lack of military capabilities, not their lack of will to do the Union harm.
I have always thought that the Confederates never should have conducted any offensive raids. They were just wrong morally and tactically. They shouldn’t have fired on Fort Sumter either.