Can’t invade your own country. The south was taken over by rebels. And, as George Washington did to the Whiskey rebellion, Lincoln did to the southern rebels.
Also those southern rebels committed a bunch of hostile acts, before Lincoln was even inaugurated.
December 27, 1860—South Carolina seizes Fort Moultrie, Castle Pinckney, a Federal schooner and other Federal property.
December 30, 1860—South Carolina seizes the Federal Arsenal at Charleston.
December 31—South Carolina seizes the U.S. post office and the Customs house in Charleston.
January 3—Georgia seizes Fort Pulaski to prevent U.S. troops from garrisoning it.
January 4—Alabama seizes the US arsenal at Mount Vernon.
January 5—Alabama seizes Forts Morgan and Gaines.
January 6—Florida seizes the Apalachicola arsenal.
January 7—Florida seizes Fort Marion.
January 9, 1861—In Charleston, southern guns fire on the Star of the West as it attempts to re-supply Fort Sumter.
January 10, 1861—Florida demands the surrender of Fort Pickens (refused).
February 18, 1861—Jefferson Davis is inaugurated as president of the Confederacy.
February 23, 1861—President-Elect Abraham Lincoln merely a
No significant violence involved in any of those incidents. In most cases, they simply walked in and took over. Not unreasonable since it was their own property after they declared independence.