I think what made the Spanish flu worse was the fact it happened when US troops were spreading the disease around war-ravaged Europe at a very high rate.
It wasn’t “US troops spreading it”. It is not even certain to this day exactly where it began. But troops from everywhere spread it. And the hagiography is so mixed in with wartime propaganda that it is probably impossible to unravel it today.
Even the name spanish flu reflects that fact that the outbreak could not be reported on in allied nations. It was legal to call it “Spanish”.
All the European powers had a presence in China and had trade back and forth. It’s considered likely that it started there and God only knows who brought it to war ravaged Europe.
“I think what made the Spanish flu worse was the fact it happened when US troops were spreading the disease around war-ravaged Europe at a very high rate.”
And, there were no antibiotics.