alt Hacker NewsBefore the second WW, mathematics was moving at much faster paces than after WWII, when many theories became more or less settled and only their practical applications continued to develop at a fast pace.
The modern variants of some branches of mathematics like topology or the theory of tensors have appeared during the first WW (e.g. the book of Felix Hausdorff, "Grundzüge der Mengenlehre"). Especially topology had a great influence on almost all other branches of mathematics, prompting them to reformulate many things in more general frameworks.
Therefore, by the end of WWI, it was true that many older mathematics manuals were considered obsolete, so they felt the need to write new manuals, brought up-to-date.
What you're saying make sense, but it doesn't help me understand the connection between people dying in WWI and the lack of recent textbooks. The two people the article describes as having the initial conversation were 30 and 28 years old (give or take a year each) in 1934, which is fairly young for a professor by modern standards, but this means they also presumably had been doing mathematics for around a decade each at this point. Did they not have any older colleagues at all who could have written textbooks? Why didn't they write textbooks in that time period when there would have been ones published in other languages outside of France? I'm not doubting the accuracy of the history being given here or in the Wikipedia article; like I said in my initial comment, I just don't think it's being explained very well, because there's still a gap for me between "lots of people died in the war" and "15 years later there are no textbooks".