Writing in his journal after the Civil War, Alexander Stephens, vice president of the Confederacy, declared that Southern states seceded, to no small extent, because Northern states had betrayed their "Constitutional obligations as to rendition of fugitives from service."

Historian Andrew Delbanco agrees. He acknowledges that "no one can say exactly" where conflicts over the enforcement of fugitive slave laws rank among the forces dividing the North and the South. But those conflicts, he claims, contributed mightily to a collapse of "comity" and pushed the nation toward Civil War.

In "The War Before the War," Delbanco, a professor of American studies at Columbia University in New York, provides a compelling, elegantly written account of how fugitive slave laws laid bare "the moral crisis" in the hearts and minds of antebellum Americans.

As he assesses the responses of politicians, political activists, judges and public intellectuals, Delbanco warns against "outcome bias." What seems so clear to us in retrospect, he emphasizes, was not at all clear at the time.

Those who indict compromisers or moderates as fearful, indifferent, self-absorbed or contemptible, and who credit radicals for "flair and foresight," know what Americans then did not know: Southern states would secede; a war to preserve the Union would become a war against slavery; and in the end, emancipation rather than "worse enslavement" would prevail.

Seen in this light, Daniel Webster's speech supporting the fugitive slave legislation in 1850 — although it was silent on the bill's impact on blacks — "might have been the moment that saved the nation from secession, or, at least for a decade, staved it off."

Along with concerns about history as hindsight, "The War Before the War" hears "echoes in our time" in debates over fugitive slave laws. The book includes past-in-the-present references to gun control, same-sex marriage, the Iraq war, political gridlock, echo chamber media, filmmaker Quentin Tarantino, ethnic cleansing and discrimination against immigrants. Many of them, alas, involve little more than brief homilies to ideological soul mates.

That said, Delbanco is on target, in my judgment, in reminding us of the devastating impact of "America's original accommodation with slavery." And in suggesting that these days, millions of impoverished people are out of sight and mind, much as blacks were in the 19th century, "until some shocking incident or anguished plea give them a moment's visibility before they vanish again."

Moreover, who can disagree with his conclusion that after the Union was restored "the vast work of repairing its human devastation had barely begun"?

Glenn C. Altschuler is the Thomas and Dorothy Litwin professor of American studies at Cornell University.

The War Before the War
By: Andrew Delbanco.
Publisher: Penguin Press, 453 pages, $30.