The Devastating Effects of Diseases on the Civil War Battlefield


By Professor Gary Gallagher, Ph.D., University of Virginia

While most history textbooks on the American Civil War emphasize on the fight between two major armies, the Union and the Confederacy, few focus on the silent “Third Army” of the war: infectious disease. Invisible as the army may have seemed on a macroscopic level, it proved devastating on a microscopic level. Two-thirds of all the 660,000 deaths during the war can be attributed to disease.

Brandy Station, Va. Field hospital of the 3rd Division, 2d Corps.
Brandy Station, Va. field hospital of the 3rd Division, 2d Corps. (Gardner, James; Civil War Glass Negatives/Public domain)

A Historian’s Perspective on Disease During Wartime

Historian Jeffrey S. Sartin writes about this invisible legion of doom in an article entitled “Infectious Diseases During the Civil War: The Triumph of the ‘Third Army’” (1993). According to Sartin, “The American Civil War represented a landmark in military and medical history as the last large-scale conflict fought without knowledge of the germ theory of disease.”

While smallpox vaccines were already a reality, other epidemics – strengthened by unsound hygiene, dietary deficiencies, and battlefield wounds – raged uncontrollably during the American Civil War. Overall, Sartin lays out some disturbing numbers in his path-breaking article. He states: “The scorecard on major illness during the Civil War is numbing in its enormity. Among Union soldiers, pneumonia (including influenza and bronchitis) accounted for 1,765,000 episodes of illness and 45,000 deaths; typhoid for 149,000 episodes and 35,000 deaths; diarrhea/dysentery for 360,000 episodes and 21,000 deaths; and malaria for 1,316,000 episodes and 10,000 deaths.”

According to this thesis, the Third Army was even more successful than the Confederate Army in its “kill missions”. High rates of disease-related mortalities made this Third Army one of the greatest unmatched militias in history.

Learn more about the common Soldiers in the American Civil War.

Primitive Medical Practices During the Civil War

Patients in Ward K of Armory Square Hospital, Washington D.C.
Patients in Ward K of Armory Square Hospital, Washington D.C. (Image: Civil War Glass Negatives / Public domain)

And medical practices sure didn’t help. Without the advancements of blood tests, X-rays, or microbiological cultures, Civil War doctors had to notoriously resort to medieval approaches to combat injury and illness. Tattered soldiers became amputated veterans; their limbs were sawed off with primitive farm tools.

Advancements in medicine had not yet caught up with the industrialized progress of mortars, cannon, and rifles. As these weapons became more indiscriminant and efficient, American medicine remained a relic of the past. Civil War surgeons had inaccurate views of the origins of diseases, so they typically made matters worse with primitive bloodletting practices and poisonous tonics.

As Sartin reminds readers, “Army surgeons knew of few effective treatments and so put their faith in a variety of misplaced therapeutics…Opium and whiskey were freely administered [and] toxic doses of the mercurial agents calomel and “blue mass” often resulted in loss of teeth and hair, renal damage, and (rarely) gangrene of the oropharynx and death.” In essence, medical practitioners did little to stop diseases as they do so well in the twenty-first century. Instead, they antagonized and even promoted health risks.

The growth of the field of photography in this era helped budding photographers like Timothy H. O’Sullivan make careers off capturing the horrors of the American Civil War and its gruesome medical practices. Their photos are more akin to something that should be placed in a haunted house than something that should be reflective of medical history. 

The Emancipation Proclamation

By January 1, 1863, the Emancipation Proclamation was officially signed. It stated that “[a]ll persons held as slaves within any States…in rebellion against the United States, shall be then, thenceforward, and forever free.”

This newfound freedom excited blacks across North America and the Caribbean, encouraging thousands to join the earliest authorized “colored regiments” in Massachusetts, Tennessee, and South Carolina. Abolitionists like Frederick Douglass again applauded these civil rights gains, as black enlistment blossomed to 180,000 in total by the end of the war. In total, they made up nine percent of all men in uniform.

Black women assisted their newly-enlisted brothers, fathers, uncles, cousins, neighbors, and sons by joining nursing and scouting efforts. Black women could not officially join the military, but hundreds of thousands of newly-emancipated black women helped out in alternative ways.

Learn more about the crisis at Fort Sumter.

The ‘Third Army’ of the American Civil War

Sartin, however, is not the only scholar familiar with these travesties – the devastation of the Third Army is also highlighted in a recent lecture on the American Civil War recorded for The Great Courses. The lecture goes to describe the psychological wounds that shadowed the epidemiological disasters of the American Civil War.

It states: “Some men had horrible diseases. Some had horrible wounds and lived, but they lived in spite of the medical care that they got in many instances rather than because of it. In fact, many soldiers would write home in their letters and put in their diaries that they would rather remain in their tents and try to battle out a terrible bout of this or that disease or try to recover from one of their wounds on their own than put themselves into the hands of the surgeons and go into the hospitals where they thought they would probably not have as good a chance of surviving as they did on their own. Unfortunately, there was more than a little bit of truth in that.”

This is a transcript from the video series The American Civil War. Watch it now, Wondrium.

The bottom line is that the so-called “childhood diseases” (i.e., measles, mumps, etc.) that we inoculate on a regular basis today, were the devilish soldiers of the Third Army during the American Civil War. They mowed through forces with biological precision; they helped create a blitzkrieg of bacteriological infliction that changed the course of the war.

The Third Army played a major role in halting several major campaigns. These delays, coming at crucial points in the conflict, prolonged the devastating conflict between North and South by as much as two years. Put simply, the Third Army may very well have been the most dominant force in the Civil War.

Common Questions About Disease in the American Civil War

Q: How many soldiers died from infectious disease during the American Civil War?

Roughly two-thirds of the total 660,000 deaths during the American Civil War were caused by infectious disease.

Q: What types of infectious diseases were responsible for the massive amount of deaths during the American Civil Wars.

All sorts of infectious diseases devastated populations, including such common diseases as: pneumonia, typhoid, diarrhea/dysentery, measles, mumps, malaria, and influenza.

Q: Why couldn’t doctors help prevent these infectious diseases?

While doctors tried to prevent these infectious diseases, they were usually unsuccessful due to lack of knowledge of the germ theory of disease. Medical advancements were sluggish in comparison to advancements in weapon technologies.

Q: Why is infectious disease sometimes referred to as the Third Army of the American Civil War?

It mowed through forces with biological precision; they helped create a blitzkrieg of bacteriological infliction that changed the course of the war. It may have been silent, but it was more efficient in killing its enemies than both the Union and Confederate armies.

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