This is a harsh, satirical poem that means just the opposite of what it says - so this is an example of "contrast". There is the use of "apostrophe" because the poet addresses three people that are not present, the maiden, the child and the mother - all people who suffer when their "men" are killed by war, and yet, war is kind -- NOT! There is a lot of imagery - for one, there is the image of death, presented by the following:
Because your lover threw wild hands toward the sky
And the affrighted steed ran on alone
We see that the maiden's love died - probably shot, fell off the horse, and the horse ran on.
There is an example of personification:
Hoarse, booming drums of the regiment,
Drums can boom, but they cannot be "hoarse" because they are not human.
There is a metaphor:
Great is the battle-god, great, and his kingdom -
A field where a thousand corpses lie
The "kingdon" of the battle god is the field of battle where thousands lie dead.
Pretty grim, huh?
There is alliteration:
tumbled in the yellow trenches
"tumbled" in the "trenches"
Also, more alliteration:
heart hung humble
You can go through the poem and pick out more images, metaphors, etc.
I HATE this poem because my son is in the Navy, currently deployed, so it is hard to read -- but, that's the point. It evokes emotion, wouldn't you agree?