"1914" contains many examples of alliteration. Take the first two lines, where dramatic, whooshing /w/ sounds add intensity to the speaker's language and, in doing so, emphasize the destructiveness of war:
War broke: and now the Winter of the world
With perishing great darkness closes in.
That /w/ occurs again in line 4 ("width of Europe whirled") and line 13 ("wild Winter"), making it a kind of sonic through-line in the poem.
In the poem's octave (or first eight lines), several other repeated consonant sounds contribute to the punishing overall sense of war's destruction. In line 5, for example, the speaker repeats the guttural /r/ sound across a strong mid-line pause, or caesura, reflecting the rip in the "sails of progress." The assonance of the short /eh/ sound adds to the echo on either half of the line:
Rending the sails of progress. Rent or furled
Likewise, the speaker repeats /f/, /th/, and /h/ sounds in lines with strong caesuras, subtly reminding of the way war breaks society—as well as the lines and repeated sounds of this poem—apart:
Famines of thought and feeling. Love's wine's thin.
The grain of human Autumn rots, down-hurled.
Alliteration doesn't always mean doom and gloom, however. Parallel /s/ and /bl/ sounds ("Spring had bloomed" and "Summer blazed") help to signal the sonnet's turn to an atmosphere of relative peace, prosperity, and harmony. Likewise, line 11's "harvest home" takes the bitter, despairing /h/ of line 8 and makes it glad.
Of course, this detour into gladness doesn't last long. While "1914" suggests some hope for society's renewal through the blood sacrifice of war, the speaker doesn't seem extremely optimistic or see much reason for celebration. Nothing indicates the speaker's feelings more strongly than the return to strong, ominous alliteration in the poem's last lines:
But now, for us, wild Winter, and the need
Of sowings for new Spring, and blood for seed.