The Calculus of Violence: How Americans Fought the Civil War
by Aaron Sheehan-Dean
Harvard University Press, 2018

For a few days in late April 1862, the city of New Orleans lay in turmoil. Union naval forces under the command of Flag Officer David Farragut controlled the Mississippi, but ground troops led by Major General Benjamin Butler didn't occupy the city until May 1. In the interim, attempting to subdue a surly population and pressure city officials to surrender, Farragut ordered a small contingent ashore to hoist the stars and stripes as a signal of U.S. control. The men warned onlookers that anyone molesting the flag would be dealt with, but when they returned to their ship, they left it unprotected. The suave William Mumford, a favorite of the city's gamblers, pulled it down minutes later, and no doubt reveled in notoriety until Butler arrived. Thereafter, he was arrested, tried, and hanged.

Mumford's death was a cause célèbre, and to Aaron Sheehan-Dean, who recounts the story in The Calculus of Violence: How Americans Fought the Civil War, the controversy surrounding it illustrated both sides' obsession with a war fought by rules. For Southerners, Mumford's "murder" was an outrageous, if predictable, outgrowth of the North's wanton disregard for established norms. For the North, he was a rebel whose hanging was a necessary, if unfortunate, means of maintaining order. Butler insisted that the flag had signaled the end of violence, so when Mumford pulled it down, he put the city in danger of renewed destruction. But when Robert E. Lee complained by letter to George McClellan, he argued that New Orleans was not under Union jurisdiction at the time of Mumford's action and, in any event, prisoners should not be hanged. McClellan sympathized with Lee, but Lincoln let the matter drop.

For Sheehan-Dean, the fact that enemies still fired lawyerly arguments at each a year into bloodshed underscores the degree to which they inhabited a universe of moral limits. The laws of nature and nature's God applied even to war, and certain actions remained unthinkable in the midst of slaughter. Civil War historians who write of violence as an "autonomous force" overstate their case, Sheehan-Dean writes. Yes, tactics did become more destructive over time, but responsible people on both sides felt obligated to justify each step, and as deadly as the war became, it was never as bad as it could have been.

Much of The Calculus of Violence recounts the methods by which Americans restrained violence. Some are surprising. For example, "retaliation" probably conjures images of tit-for-tat vengeance, but Sheehan-Dean argues it limited violence. To 19th-century Americans, retaliation meant measured response, repaying the enemy exactly what had been delivered, so it was thought to disincentivize escalation. More predictably, diplomacy constrained the bloodshed, as well. Tradition held that captured regulars should be kept alive, but irregulars and privateers could be executed summarily. In practice, however, Lincoln hesitated to kill irregulars because he feared the South would do the same to Union prisoners. Finally, there were the two-edged swords of race and nation. On the one hand, they caused the crisis. Southerners thought slavery belonged to a "natural" racial order, and Northerners defined the Confederacy as an insurrection against which the Constitution sanctioned violence. On the other hand, race and nation could limit violence. That whites feared comparison to "uncivilized" Native Americans prevented some atrocities, and Appomattox ended the war, in part, because both sides accepted the legitimacy of the Confederate state's surrender.

There is merit in Sheehan-Dean’s approach. The more we think of violence as having a life of its own, the more we are apt to forget about the human choices leading up to it. Yet despite his many examples, the choices for restraint he highlights are not always convincing. Part of the problem is a matter of cause and effect. Did the laws of war really restrain warring Americans, or did warring Americans wear laws like fig leaves to excuse what they did? And at what point do laws undergo so much revision that they functionally serve as no laws at all? Some of the bloodthirstiest cries came from abolitionists, who, ironically, held pacifism an absolute before the war, and if military necessity could justify Nathan Bedford Forrest's slaughter of captured soldiers at Fort Pillow in 1864 – and Jefferson Davis accepted that it did – one wonders what would have been going too far. Another problem is the sponginess of "restraint." At times, Sheehan-Dean, like Butler in New Orleans, seems to see restraint in any choice not to use greater violence. But often greater violence was unnecessary or would have been counterproductive. If, for example, the Union banished rather than killed hostile civilians not because of the laws of war but because its objective was to reunite with them after the war, was it really restraining itself or was it simply matching means to ends?

The Calculus of Violence is most successful at restoring the often tortured justifications both sides trotted out to convince themselves they were making the right choices. Unfortunately, it’s not always clear that mattered. Because both sides weighed their actions in the context of how they expected the other side to act, and because the objective of both was to suppress the will of the other, it was easier for violence to ratchet up than down. That may not have made it an "autonomous force," but it did give it a momentum that even lawyers and moralists struggled to contain.

Kip Wedel is an associate professor of History and Politics at Bethel College in North Newton, Kansas.