Soviet Union lost 20 to 27 million people during WWII, which amounts to 10-15% of entire population at the moment.

https://en.wikipedia.org/wiki/World_War_II_casualties_of_the...

And terrifying graph for percentage losses by country:

https://topforeignstocks.com/2016/04/19/chart-world-war-ii-c...

Yep, that does stand out as a historical exception. But even a once off 15% reduction over a few years isn't necessarily going to matter much in the face of sustained exponential growth - if it happened in Ethiopia, the population would recover within 5 years.

Before people moved around a great deal, war was the most effective way to spread disease. USA's entry into WWI spread "Spanish" Flu from rural Kansas to the world, killing between 17 and 100 million.

Highly contagious diseases have inevitably spread worldwide for centuries now, ever since ships got fast enough. Wars only accelerate the process slightly, which hardly matters in the long run. There was another worldwide respiratory virus pandemic starting in 1889 which killed a lot of people despite the lack of large-scale wars.

https://doi.org/10.1016/j.lpm.2022.104111

Assuming that the "Spanish Flu" originated in the USA (possible but unproven), it would have spread everywhere even if we never entered WWI.

That link appears to describe an earlier epidemic that did not coincide with a world war and killed far fewer people; what is the relevance of that?

It is well known that "Spanish" Flu originated in Kansas. It certainly would have spread beyond in the absence of USA military action, but it also certainly would not have killed 100 million people. Exposure rate drives incidence rate, which in turn drives mortality. If only ten people in a location have been exposed and only one of those has become infected, the resources of that location are better able to cope with the epidemic than would be the case if 1M were exposed and 100,000 were infected. Both treatment and isolation are more successful with more resources. This was why Americans were urged to isolate in the initial stages of covid, to prevent a shortage of hospital beds.

A very wrong way to handle an epidemic is to transfer tens of thousands of people to ground zero, expose them for weeks, and then transfer them to various other continents.

Our #1 export is death.

That’s why this line of thought is shunned. It’s because the best historical precedent for intentional population reduction is not war, it’s genocide.