A couple of years ago, I had the honor of publishing American Secession: The Looming Threat of a National Breakup by Frank Buckley, a prolific author and law professor at George Mason University. Buckley began by noting the obvious: that we in America are more divided now than at any time since the 1850s. We know how that Disunited States of America worked out, and the horror of the Civil War—what Buckley calls Secession 1.0—has led many of us to conclude that we’d put up with almost anything rather than risk a repeat of that disaster. “Almost” anything. Buckley does...