We can in part attribute some of the increases to the length of time and development of technology in between wars. For example- the weapons and tactics used in the American civil war were largely more efficient at creating massive casualties. Of course when we look at WW2, a war separates by quite some time and technology, the first “modern war” using destructive technology of unprecedented magnitude on an unprecedented scale in history, or at certain large scale modern conflicts, the organized combatant deaths are actually lower for many individual forces or total engagements. How do we explain this? Well- technology. Many civil war deaths were from secondary causes, treatable illness, infection, malnutrition, exposure, etc. As opposed to direct aggressive means. The knowledge to injure and kill outstripped the knowledge to save lives and ensure general health and hygiene on the battle field and/or the technology and resources to make supplies and personnel available.
People often misunderstand average lifespans- they think that if an era of history had an average lifespan of 40 for example, that in that time people rarely lived to be “old” or that increasing average lifespan means someday people will live to be 300 years old as a natural progression. Average lifespan includes things like infant and child fatalities. A simplified version is this: if 4 people are studied as a group and 2 live to be 60 and 2 die at birth (0), the average lifespan would be very low even though half the people lived to 60. It’s also important to note that often times, the odds of surviving into old age increase dramatically IF a person survives childhood. So the average lifespan for a random person in a group may be 30, but if they live to 20 they may have an 89% chance to live to be older than 70. This same principle is important in understanding fatalities in conflicts of different periods.
The bullets used by “primitive” guns like those of the revolutionary war were just as if not MORE deadly and devastating than most any single bullet from common modern “hand held light weapons systems” like battle rifles etc. These older weapons had generally poorer accuracy or consistency in accuracy, and they generally had much lower rates of fire. In a given period of time they could not output as many projectiles (like bullets..) as many more modern weapons. So your odds of being hit by a projectile decreased dramatically with range and your overall odds of being hit by a round were generally lower in most equal circumstances due to there being less ability to sustain a volume of fire. If you were hit, the odds of any particular severity of impact being critical were generally higher. Many common tactics of the day would increase the chances of getting shot vs. modern tactics, so some of the odds advantages for avoiding projectiles due to weapons design etc. were mitigated.
Where things become important is when one is shot. The projectiles used in common revolutionary war era weapons tended to be large and heavy and carry great deals of kinetic energy from mass. A projectile penetration which may be non critical with a more modern weapon might shatter bone or otherwise cause serious critical inerrant injury from sheer force and mass impacting the body. As time has progressed up into the current day, small arms weapons systems have tended to favor using accuracy and/or rate of fire coupled with increasingly smaller but higher velocity projectiles to inflict damage. There are numerous reasons for this which we will not discuss at this time, but while a smaller and faster moving projectile may carry the same overall kinetic force as a larger and slower one- the way those projectiles behave when striking matter is generally different, so the types of wounds and various strengths and weaknesses of each varies and the projectile or cartridge are chosen based on
The circumstances and theoretical use case at the time they are selected. By the time the American civil war came around, fully automatic feed weapons aka “machine guns” and “Gatling guns” we’re in existence. Man portable explosive ordinance and anti personnel means were reasonably common. Long guns aka Rifles capable of long range accurate and deadly fire existed and pistols or personal defense weapons with high rates of fire were common.
Those and many more technologies of death contributed to the attrition of the civil war as well as the spread of industrialization allowing for the mass production and distribution of relatively precision goods which previously wouldn’t be possible at such scales.
In all of that however, the science of medicine and protection had increased relatively little in a practical sense. Contrast that to more modern conflicts where the rate of fatality for most given injuries is FAR lower than it was in the civil war era, and you have a better picture.
If it still doesn’t add up I will put it another way.
In some “Queens and Castles” age where the deadliest weapons available to a soldier are spears and swords- the number of people any one soldier can kill with their weapon in a battle is probably lower than the number a skilled soldier can kill with a modern riffle. That said- those wounded by a modern riffle in a conflict involved equipped and developed combatants will generally have much more sanitary conditions, access to staple needs, and advanced life saving technology. Those in the sword age have a high chance of dying in the way to the battle from lack of nutrition or other causes linked to the level of technology and development. A sword and a riffle are just as deadly to a single person on the recieving end, but the quality of care and the conditions make a difference- and the overall health and ability to maintain and protect the health of soldiers comes in to play.
Lastly- we can say that many are STILL sympathetic to the Confederacy or believe the war is not over to this day, so the capitulation of one side of the other over an issue or of defeat can impact casualties. When someone decides a goal is not worth the price or that a war is lost and further fighting is simply squandering lives etc. a conflict may end. The value placed on lives vs. the issue of the conflict has a tendency to influence things too.
Those and many more technologies of death contributed to the attrition of the civil war as well as the spread of industrialization allowing for the mass production and distribution of relatively precision goods which previously wouldn’t be possible at such scales.
In all of that however, the science of medicine and protection had increased relatively little in a practical sense. Contrast that to more modern conflicts where the rate of fatality for most given injuries is FAR lower than it was in the civil war era, and you have a better picture.
In some “Queens and Castles” age where the deadliest weapons available to a soldier are spears and swords- the number of people any one soldier can kill with their weapon in a battle is probably lower than the number a skilled soldier can kill with a modern riffle. That said- those wounded by a modern riffle in a conflict involved equipped and developed combatants will generally have much more sanitary conditions, access to staple needs, and advanced life saving technology. Those in the sword age have a high chance of dying in the way to the battle from lack of nutrition or other causes linked to the level of technology and development. A sword and a riffle are just as deadly to a single person on the recieving end, but the quality of care and the conditions make a difference- and the overall health and ability to maintain and protect the health of soldiers comes in to play.