The thing with war is that, while it can certainly kill a lot of people, they tend to take a fair amount of time to kill the multitude of people they kill. WW2 killed a total of some 420 000 US citizens, but it did that over a period of nearly 4 years, and I would be very surprised if more than 400 US citizens died on average per day. Individual battles definitely killed thousands at a time, sometimes in hours or minutes when things like capital ships got sunk, but there were also long stretches of the war where the fighting hardly killed any US citizen.
And the USA has the advantage of only the smallest parts of their territory being assaulted and thus their general public not being at risk. Nations where the fighting occurred have seen much greater casualty numbers in absolute numbers and relative to their population simply because the civilians were at risk of a stray bullet or shell. Or deliberate action.
Infectious diseases, however, once they get in and isolation and quarantine become impractical if not impossible? Well, as COVID-19 is demonstrating, it can kill hundreds of people within hours. The real question becomes how much of the relative population was killed by the disease, and that's something that will be hard to estimate until we start collating numbers and compare them to the numbers of previous years.
And the USA has the advantage of only the smallest parts of their territory being assaulted and thus their general public not being at risk. Nations where the fighting occurred have seen much greater casualty numbers in absolute numbers and relative to their population simply because the civilians were at risk of a stray bullet or shell. Or deliberate action.
Infectious diseases, however, once they get in and isolation and quarantine become impractical if not impossible? Well, as COVID-19 is demonstrating, it can kill hundreds of people within hours. The real question becomes how much of the relative population was killed by the disease, and that's something that will be hard to estimate until we start collating numbers and compare them to the numbers of previous years.