Today I did what I often do, i.e I started browsing Wikipedia. On today's Main Page I clicked on the https://en.wikipedia.org/wiki/Invasion_literature link, which describes a sub-genre of fiction that was thriving towards the end of XIX century, when the continental Europe apparently lived in fear of the German invasion.
The novella which sparked off the furor was https://en.wikipedia.org/wiki/The_Battle_of_Dorking by https://en.wikipedia.org/wiki/George_Tomkyns_Chesney
Here's the link on PG https://gutenberg.org/ebooks/65882 (around 25k words)