Google Books Ngram Viewer allows you to track the usage of words or phrases over time from a vast library of books. The data is then normalised by the number of publications released in each year. This accounts for the rarity of publishing during the 16th and 17th centuries and allows you to search back relatively far.
Here’s a plot of the use of “war” which reveals some obvious spikes.
Use of the tool also reveals a quite sad story of the decline of the use of “nature” in publishing, although the use of “wildlife” and “environment” have increased.
Arguably, the more common use of the word environment is probably linked to the progressively dawning realisation of the issue of climate change over the last century, while wildlife is perhaps a more recent term – especially when you look at the use of the more archaic flora and fauna.
Interestingly, whatever the search it seems there are always either spikes or dips around the two World Wars, even in some arguably irrelevant words or phrases.
However, the relative jump in key phrases at these times would skew the overall use of others down – remember the data is normalised relative to the number of books being published. Even if there are the same number of books being published on the topic of nature, increasing the usage of that word, the books related to war, and their linked content would skew it down regardless.
Definitely worth a little play around with…