[Bigg Red]

Isn’t it true that Kipling wrote the poem after his son was killed in WWI?

[AnAmericanMother]

No, but as a man of great imagination he feared all the time what did, inevitably, happen. (They said that you had to keep moving at the Somme to survive, because every square foot of ground was hit at least twice.)

Kipling's poem was a header (a custom of his) to the chilling revenge tale "Mary Postgate" (don't read it before you go to bed) which was published in the Pall Mall Magazine for September 1915. John Kipling was reported "missing presumed dead" a few months later.