Human devastations often follow each other. War leads to impacts that make people susceptible to other conditions as people suffer dislocation, cold and starvation. World War One was followed immediately by the devastating flu epidemic, then the Great Depression, then World War Two. Over three decades of (mostly human-created) awfulness.
Notes and sources
The Great War and mortality impacts: Dmitri Jdanov, Evgeny Andreev, Domantas Jasilionis and Vladimir M Shkolnikov of the Max Planck Institute in 2005. Between 1913 and 1918, British men aged 23 showed a 15-16 fold increase in the probability of premature death.
https://www.demographic-research.org/volumes/vol13/16/13-16.pdf
During World War One, in 1916, the Newfoundland Regiment went into action 753 strong; the following day, only 68 answered the roll call – 90% casualty rate, of whom almost half were deceased. In military (and any, actually) terms, this was a catastrophic and devastating loss.
http://www.heritage.nf.ca/first-world-war/articles/beaumont-hamel-en.php