In a lot of ways, the men (and small numbers of women dressed as men) who fought the American Civil War had the worst of both worlds: They were fighting (especially in Phase II, 1864-1865) a modern industrial war; but unlike their counterparts in World War I, didn't have the benefits of modern medicine. It did not have to be thus: the "pieces" of modern medicine were lying around Western civilization for a very long time--microbes had been known about since the 1600s, bacteria from the early 1800s;before being assembled, quite quickly, very soon after the ACW into something instantly recognizable to us 21st-century types. The two biggest things that would have helped Billy Yank and Johnny Reb in practice: antiseptic procedures, and modern field sanitation.
There's most likely a single POD in the 1830s or 1840s that would bring the whole package to America before Fort Sumter, but I can't puzzle it out. So I'l cheat a bit and do a twofold POD: 1) Germ theory shows up in France, a single generation before it did OTL, and is transmitted to American medical schools via academic vectors; and 2) the British Army figures out the basics of field sanitation during the Crimean War. There's an extremely clear vector for that one: Gen. George McClellan was the U.S. Army's official observer there, and for all his faults the man was an excellent organizer and instiller of discipline (a necessary component of field san. even today), and cared about the welfare of his troops. Let's leave triage out and say it was developed as OTL, i.e. by Jonathan Letterman and pals in 1861 and 1862. So by the time Antietam is over, the Union at least has as good a medical system (with one key shortfall, to be discussed later) as the British Army had in 1914 (although horse-drawn ambulances instead of lorries, but that's barely a disadvantage given the primitive state of motor transport in '14).
This is by no means a trivial change. In the Civil War, roughly 2 Union soldiers died of disease/non-battle injury (DNBI) for every one that was Killed in Action (KIA) or died of wounds (DOW). In World War I, roughly 17 British soldiers were KIA/DOW for every 1 DNBI. Now, the ratio wouldn't be quite as high: fewer ACW soldiers will be KIA/DOW because of the absence of machine guns and barbed wire; and more will still be lost to DNBI because, even if Union doctors understood the malaria vector and mitigated it through field san., they still couldn't treat it until quinine was invented (that, plus the fact that Belgium and northern France aren't anopheles country, is the big advantage that solders in WW1 would still enjoy). So let's say that there's "merely" a reversal of the ratio and that ATL, 1 Union soldiers is DNBI for every 2 KIA/DOW. Even if the Confederates maintain the same ratio (they might; because although their triage system was weaker, their doctors were probably about as good *and* their folks didn't die of malaria nearly as often due to 'seasoning'), this is still a massive advantage for the Union.
So, obvious result: Union wins faster. But are there any *other* major impacts?
There's most likely a single POD in the 1830s or 1840s that would bring the whole package to America before Fort Sumter, but I can't puzzle it out. So I'l cheat a bit and do a twofold POD: 1) Germ theory shows up in France, a single generation before it did OTL, and is transmitted to American medical schools via academic vectors; and 2) the British Army figures out the basics of field sanitation during the Crimean War. There's an extremely clear vector for that one: Gen. George McClellan was the U.S. Army's official observer there, and for all his faults the man was an excellent organizer and instiller of discipline (a necessary component of field san. even today), and cared about the welfare of his troops. Let's leave triage out and say it was developed as OTL, i.e. by Jonathan Letterman and pals in 1861 and 1862. So by the time Antietam is over, the Union at least has as good a medical system (with one key shortfall, to be discussed later) as the British Army had in 1914 (although horse-drawn ambulances instead of lorries, but that's barely a disadvantage given the primitive state of motor transport in '14).
This is by no means a trivial change. In the Civil War, roughly 2 Union soldiers died of disease/non-battle injury (DNBI) for every one that was Killed in Action (KIA) or died of wounds (DOW). In World War I, roughly 17 British soldiers were KIA/DOW for every 1 DNBI. Now, the ratio wouldn't be quite as high: fewer ACW soldiers will be KIA/DOW because of the absence of machine guns and barbed wire; and more will still be lost to DNBI because, even if Union doctors understood the malaria vector and mitigated it through field san., they still couldn't treat it until quinine was invented (that, plus the fact that Belgium and northern France aren't anopheles country, is the big advantage that solders in WW1 would still enjoy). So let's say that there's "merely" a reversal of the ratio and that ATL, 1 Union soldiers is DNBI for every 2 KIA/DOW. Even if the Confederates maintain the same ratio (they might; because although their triage system was weaker, their doctors were probably about as good *and* their folks didn't die of malaria nearly as often due to 'seasoning'), this is still a massive advantage for the Union.
So, obvious result: Union wins faster. But are there any *other* major impacts?
is in there favor they already had a huge pop advatge .the add on the souths might help more. it will still end with the union victory but it might be a few months to a year and a half later than OTL.