The Table above compares deaths by combat and deaths by disease. You can take these numbers with a grain of salt.
Many of the deaths shown for wars were likely by disease.
In the Civil War far more soldiers died from disease than from combat. I broke those deaths out by US and Confederate and combat and non combat, mostly disease.
The Spanish Flu was by far the greatest killer. Many of the deaths described to WWI were likely Spanish Flu Deaths.
"Far more of the country's military personnel perished from infectious diseases than from enemy action. This enduring feature of war was finally reversed in World War II, chiefly as a result of major medical advances in prevention (vaccines) and treatment (antibiotics). Safeguarding the health of a command is indispensable for the success of any campaign. Wars are lost by disease, which causes an enormous drain on the military's resources and affects both strategy and tactics. Disease and combat mortality data from America's principal wars (1775-present) fall into two clearly defined time periods: the Disease Era (1775-1918), during which infectious diseases were the major killer of America's armed forces, and the Trauma Era (1941-present), in which combat-related fatalities predominated."