When novelists write historical fiction, they aspire to give the chaos of history coherence, for the nature of stories is to make events understandable. That clarity is the promise of books such as E.L. Doctorow's The March or Margaret Atwood's Alias Grace. But as I researched and wrote The World Made Straight, I came to know what I suspect all historical novelists eventually realize: that such forays into the past create more questions than answers, but that raising those questions is enough.

In my case, the urge to write historical fiction came from events that took place as far distant as another continent and as close as my own family.

I hoped writing the novel might lead me to a better understanding of one of the most troubling aspects of human history: the atrocities committed among people who have lived together for generations, as in Nazi Germany, Rwanda, Cambodia, Bosnia. As in Madison County, N.C., among my own ancestors, during the Civil War.

The county, known as "Bloody Madison," was evenly split between Unionists and Confederates during the war. In late January of 1863, the Confederate army sent the North Carolina 64th regiment into the Unionist hotbed of Shelton Laurel. The Confederate soldiers rounded up 15 of their neighbors and took them prisoner. Several of the captured were grandfathers; the youngest, David Shelton, was 12, his brother 15. Two prisoners escaped, but on the snowy morning of January 23, the regiment's leader, Colonial Keith, ordered the 13 others to be lined up in a meadow and shot. My great-great-great-great grandfather Dr. Joshua Candler belonged to the regiment, and his brigade may have been among those present.

It is disturbing to imagine him there, a man who had taken an oath as a physician to heal life. Before the war, had some of the prisoners been Dr. Candler's patients? If so, what had he felt as they lined up? If he was a member of the firing squad, had he deliberately missed? Or had the war so inured him to violence that he felt—either as witness or executioner—no compassion or horror at all?

As I read everything I could about the massacre, I also did research on internecine atrocities in Germany and Russia, Bosnia and Kosovo and, most of all, Pol Pot's Cambodia. In addition, I looked into my own family history and discovered that as many of my relatives fought for the Union as for the Confederacy, including Martin Rash, whose son Robert married Dr. Candler's daughter Lillie. I wanted my novel to deal not only with the massacre, but also with its continuing importance over a century to the participants' descendants.

In The World Made Straight, Dr. Candler makes two winter visits to Shelton Laurel. The first is to minister to eight-year-old David Shelton, who is near death due to scarlet fever. Five years later, Dr. Candler returns to Shelton Laurel with the North Carolina 64th. The novel's other story is set in the 1970s and centers on two of Joshua Candler and David Shelton's descendants, a down-and-out former schoolteacher and a 17-year-old high school dropout.

Now that I have finished my novel, put in it everything I learned from decades of research, I know I will never know what my ancestor might have felt at Shelton Laurel. Nor will I ever fully understand what happened in Cambodia and Rwanda. But if I failed to achieve understanding, I gained awareness. That may be the best that any work of historical fiction has to offer—not just to its author, but, more importantly, to its readers—a chance to grapple with the mysteries and complexities of the past, in hopes of seeing the present a little clearer.

As for me, I'd also hoped that writing a novel would allay an image that has haunted me for years. This image is of 12-year-old David Shelton's last moments. He is shot in both arms, his father and three brothers dead beside him. He pleads to be allowed to go home to his mother and sister. But the soldiers do their duty.

I am haunted still.