Gettysburg is located in the county next to Franklin County. Ayer focuses on Franklin County along with the Shenandoah Valley in “The Thin Light of Freedom.” (Ricky Carioti/ The Washington Post/The Washington Post)

James Oakes’s most recent book is “The Scorpion’s Sting: Antislavery and the Coming of the Civil War.” He is Distinguished Professor of History at the Graduate Center, City University of New York.

In 1991 Edward Ayers, one of our most accomplished historians of the 19th century, got the idea for a different kind of history of the Civil War. Rather than paint a grand tableau of the momentous conflict between the North and the South, he would retell the story on a human scale by focusing on two places, Augusta County in the Shenandoah Valley of Virginia, and Franklin County in Pennsylvania, 200 miles to the north. The white populations of the two counties had a lot in common. They were mostly farmers, with similar religious convictions, ethnic origins and political traditions. The one thing that made the two places fundamentally different was slavery. In 1860 one-fifth of the people of Augusta County were enslaved. By contrast, Pennsylvania’s legislature had been the first in history to pass an abolition statute, way back in 1780.

Ayers began combing through archives, lib­raries and local historical societies, eventually amassing a rich trove of sources — diaries, letters, small-town newspapers, census and tax records — sources he has generously shared online at a user-friendly website called “The Valley of the Shadow.” He has put these sources to impressive use in a two-volume history of “the war in the heart of America.” His Bancroft Prize-winning “In the Presence of Mine Enemies” appeared in 2003, covering the years from 1859 to 1863. Now comes Volume 2, “The Thin Light of Freedom.” It opens with Robert E. Lee’s invasion of Pennsylvania in the summer of 1863, takes the story to his eventual surrender at Appomattox in 1865 and continues through Reconstruction all the way up to the opening years of the 20th century.

There are hundreds of books reconstructing the lives of Civil War soldiers, women on the home front and enslaved Americans who took advantage of the war to secure their freedom. But few of them succeed as well as these volumes in capturing the day-to-day experience of the war without losing sight of military operations or the political issues at stake.

“The Thin Light of Freedom,” by Edward L. Ayers (WW Norton)

One of Ayers’s recurring themes is the terrible contrast between the beauty and agricultural richness of the valley and the violence and bloodshed of the war and its aftermath. His description of the burning of Chambersburg, Pa., by Confederate troops is compelling, chilled by new details he has uncovered. His account of Union Gen. Philip Sheridan’s destructive sweep through the farms and fields of the Shenandoah Valley concludes with the equally chilling observation that, judged by the military objectives Ulysses Grant set for it, the campaign was a failure.

The irony, for Ayers, is that as the war became more brutal, its moral significance became clearer. He believes that the Yankees embarked on their crusade with no purpose other than to restore the Union. By the time “The Thin Light of Freedom” opens, however, the North had committed itself to the complete destruction of slavery. Even so, Ayers stresses, when the war ended a majority of slaves were still enslaved, and it was not until the ratification of the 13th Amendment in December 1865 that complete abolition was finally secured.

Though Ayers carries his story into the opening years of the 20th century, Franklin County pretty much disappears after 1865. Pennsylvanians presumably rebuilt the lives they had before the war, but Augusta County was dramatically transformed by emancipation. White landlords struggled to negotiate new labor arrangements. African Americans searched for spouses and children and formalized their marriages. Black men voted. Black parents worked hard to ensure that their children learned to read and write, even in the most woefully inadequate schools. Gradually, white elites overturned the Reconstruction governments and justified their nearly complete takeover of the political system as a necessary readjustment of the peaceful race relations that the Civil War had supposedly disrupted. Virginians had gone to war in 1861 openly vowing to protect slavery; now they insisted that slavery had nothing to do with it.

That’s just one of the “deep contingencies,” the unpredictable turns of historical fortune, that Ayers emphasized in an earlier essay. The war itself, he wrote, was “an extremely unlikely event.” Virginians who were staunch Unionists right up to the secession crisis suddenly became ardent Confederates. Who could have imagined that a war for the Union would became a war to abolish slavery? Northerners who had never expressed the slightest concern for the civil or political rights of African Americans ended up endorsing black suffrage and the first civil rights bill in American history.

Whether these were contingent reversals or extensions of prewar patterns is hard to tell because Ayers starts his history of the war in 1859 with John Brown’s raid on Harper’s Ferry. That pretty much rules out any consideration of long-term causes. Neo-Confederate historians writing in the Lost Cause tradition also like to begin in 1859 because it makes the Civil War look like an accidental byproduct of a fortuitous event. Was it? There’s reason to doubt that the Mason-Dixon Line had always been the placid boundary that Ayers depicts. He cites the numerous Northern state votes in which substantial minorities of whites endorsed black suffrage before the Civil War. They usually lost, but it was hardly a new issue in 1864. Secessionists complained that by 1860 generations of Northerners had been taught antislavery in their catechisms, their schoolbooks, the sermons they listened to and the speeches they heard. That’s correct, isn’t it?

Ayers notes that during Abraham Lincoln’s reelection campaign in 1864, Republicans and Democrats both supported the Union, though they had very different conceptions of what the Union meant. But that was true well before the war started. The Unionism of the Virginia Whigs was always pro-slavery Unionism, so it’s not so surprising that they ended up siding with the Confederates. By contrast, Lincoln and his fellow Republicans represented a powerful strain of anti-slavery Unionism. For them the war was always about slavery and always about restoring the Union. Wars do have unexpected twists and turns, but they also exaggerate tendencies that are already there.

Fortunately for readers, such contentious issues are played out in the background, offstage as it were. Ayers set out to re-create the lived experience of the Civil War — for Northerners and Southerners, blacks and whites, men and women, soldiers and civilians — without losing sight of the political turmoil and destructive violence that affected all of them. In that he has succeeded brilliantly.

The Thin Light of Freedom
The Civil War and Emancipation in the Heart of America

By Edward L. Ayers

Norton. 576 pp. $35