Until recently, Mitchell Burford Salter had been largely lost to history. His 90-year-old grandson has rarely talked of him. His great-grandson never knew the man or his story. The name wasn't familiar when he heard it, but he agrees that the sole extant photo of the one-armed man as an adult looks remarkably similar to his youngest brother.

Some of the men whom Salter met 150 years ago in the fields and hills of southeastern Pennsylvania outside Gettysburg have been better remembered, at least among the ranks of amateur and professional historians of the Civil War. Joshua Lawrence Chamberlain, the officer lionized in Michael Shaara's Killer Angels and played in the movie adaptation by Jeff Daniels, has been credited for ordering the desperate counter-attack that saved the United States. Strong Vincent at least boasts a marker on the rocky slopes of Little Round Top, small thanks from a grateful nation for giving his life to defend his home state from cocksure Southern invaders. Both officers receive due credit in the definitive new account of Gettysburg by Allen C. Guelzo, one of the era's most renowned historians.

But even Vincent and Chamberlain are never far from disappearing into the same fog of history that had enveloped Salter. When Gettysburg National Military Park commemorated the 150-year anniversary this summer, President Obama did not visit. Neither did Vice President Biden. National television programs stayed away. Since sesquicentennial events for the Civil War began two years ago, we have seen no popular revival of interest such as what erupted in 1990 with Ken Burns' acclaimed miniseries. Still, passion for the subject hasn't altogether vanished: Guelzo's demanding scholarly account enjoyed a brief run on bestseller lists, and his book reminds us why we can't understand the ongoing but ever-tenuous American experiment unless we grapple with the events of July 1863.

Guelzo's Gettysburg: The Last Invasion is not the place to start if you have only passing acquaintance with George Gordon Meade, James Longstreet, John Buford, and the like. I made my first pilgrimage to Gettysburg when I was seven years old (shortly before Burns made Shelby Foote's voice famous and introduced the world to poor Sullivan Ballou). I have returned twice since then and read more than my share of battle accounts and Civil War overviews, including Guelzo's recent Fateful Lightning: A New History of the Civil War and Reconstruction. As an amateur student of the period, I felt while reading Guelzo that until now I hardly understood Gettysburg at all. That's a compliment, believe me. But you probably won't want to jump into such a full-dress version until you understand the broader context of the war, envision the terrain at Gettysburg, and become acquainted with the major players.

You also shouldn't dive into Guelzo's history if you're looking for a glamorized narrative of heroism and valor under fire. Yes, you will find in the detailed maze of regiment numbers and brigade commanders many such stories. You will marvel at the 1st Minnesota's suicidal charge into vastly superior numbers of Alabamians storming toward the Union center at Cemetery Ridge. You will observe Guelzo's admiration for certain standout generals: John Reynolds, who defied Meade and determined to make battle at Gettysburg, where he would perish; Otis Howard, "the Christian general" unpopular among his blasphemous peers but who understood the need to defend and hold the high ground; and especially Winfield Scott Hancock, who overcame his colleagues' disastrous errors and staved off Union collapse at the end of the second day. And even as you lament their cause, the soldiers of Virginia and North Carolina who marched with Gen. Pickett into their doom on the third day will make you gasp at what humans will do for the comrades on their right and left.

But mostly you will see Gettysburg as the generals and soldiers did: through the sulphurous haze of uncertainty. Guelzo peers into every long-standing controversy with hopes of finding light. Why didn't Dick Ewell press his advantage all the way to Culp's Hill and Cemetery Ridge during nightfall of the first day? Why didn't Longstreet begin his attack early in the next day? What could Dan Sickels have possibly been thinking by deploying his corps forward on the Emmitsburg Road instead of defending the line between Hancock's 2nd Corps and Little Round Top? Why didn't Meade heed President Lincoln and pursue the retreating Robert E. Lee and seek to end the war before he could escape back across the Potomac? Guelzo takes his best shot at answering all of these questions and many more. Neither one of the commanding generals, Meade and Lee, escapes the unforgiving scrutiny of hindsight.

Why bother revisiting these debates? More than once I've wondered whether my interest in the Civil War betrays a secret bloodlust. When I played as a child with cut-out soldiers wearing blue and gray, no one bloodied his brow. In real life, news from Gettysburg shattered families north and south of the Mason-Dixon. Consider just the Southern casualties, according to Guelzo's accounting: "Even if one takes the lowest mark, the Army of Northern Virginia suffered something comparable to two sinkings of the Titanic, the 2001 attacks on the World Trade Center and the Pentagon, ten repetitions of the Great Blizzard of 1888, and two Pearl Harbors."

Above all, Guelzo captures the fundamental reason the Civil War continues to demand attention. In his breakthrough exploration of the political machinations and personal rivalries within each army before, during, and after the fighting, he exposes stubborn traits in human nature. Larger-than-life historical figures appear limited, confused, self-absorbed. Immediately after Pickett's Charge, Lee rode up and down the line of haggard survivors and blamed himself for ordering their units' demise. Years later, he and his partisans blamed everyone else, including the men for insufficient determination to carry the colors into enemy lines. Meade, loyal ally of the deposed Gen. George McClellan, understood the political dynamics of military leadership in the snakebit Army of the Potomac. As a result, his unexpected ascent to command prompted crippling self-doubt and concern to make decisions that he could defend, whether or not they actually contributed to ending the war. Scarcely can we comprehend such responsibility for life and death—not only for the men under their command but also for the hopes and dreams of their respective peoples and governments.

Under fire we see the best and worst of ourselves. And no one saw this terrible truth more clearly than Abraham Lincoln. Guelzo's book ends where it must: with the story behind that short and surprising speech by Lincoln to dedicate the new cemetery at Gettysburg. Lincoln saw in the war not only regimental colors and flanking maneuvers but ultimately a test of national character. The battle at Gettysburg called for renewed determination, "that from these honored dead we take increased devotion to that cause for which they gave the last full measure of devotion—that we here highly resolve that these dead shall not have died in vain—that this nation, under God, shall have a new birth of freedom—and that government of the people, by the people, for the people, shall not perish from the earth."

But Guelzo, following Lincoln, understands there would be no Union without the success of its arms. And Gettysburg hinged on a host of military decisions big and small, perfectly reasonable and unfathomably irresponsible. Because the flank on Little Round Top held, because the line on Cemetery Ridge wavered but did not break, the "proposition that all men are created equal" increasingly applied over the years to the entire nation, North and South.

History sees the big picture in small events. But history also sees the small picture in big events. Unlike Col. Vincent, Pvt. Salter survived the confrontation on Little Round Top. Bayonet fixed, he advanced with the 4th Alabama toward Vincent's position on the high ground. The attack failed. His war ended that day, two years before the rest of the fighting mercifully concluded. And on that most famous patch of battlefield he left behind a relic only recently rediscovered by his family. Even now, the National Museum of Health and Medicine holds his arm, amputated at Gettysburg by a U.S. Army surgeon after the din of battle ended on the second day.

The young farmer, kin to Lincoln through the president's great-great-grandmother Hannah Salter, had joined up at the beginning of the war. By Gettysburg he had already survived First Manassas, Fredericksburg, and some of the hottest fighting at Antietam. In the end he was saved by his enemies. After returning home, he would see two sons become doctors. One started a hospital in Eufala, Alabama. In turn, one of that doctor's sons would graduate from Harvard Medical School at the end of World War II and become a surgeon in Birmingham. That surgeon would later be joined in practice by his eldest son, who never knew his great-grandfather or his story. But the records of Pvt. Salter's amputation have been rediscovered by his grateful great-great-grandaughter. And I join her, my wife, in giving thanks for this small miracle of survival in the big picture of America's most consequential battle.

Collin Hansen serves as editorial director for The Gospel Coalition. He is the co-author of A God-Sized Vision: Revival Stories That Stretch and Stir. He and his wife belong to Redeemer Community Church in Birmingham, Alabama, and he serves on the advisory board of Beeson Divinity School. You can follow him on Twitter @collinhansen.

Copyright © 2013 by the author or Christianity Today/Books & Culture magazine.
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