(Non-American here) - rather fascinating read on some American history. We hear about Lincoln, etc, but this makes it sound like Pierce was the president who effectively caused the Civil War. I'd heard the Fugitive Slave Act cited before as the trigger, and I know it technically kicked off in Lincoln's term, but the attitudes and Pierce's presidential term make it look like that's what led up to it.
He certainly was controversial during the war. Jeff Davis was his secretary of war in the 1850s. Pierce seemed close to Davis during the Civil War and supported some Confederate narratives.