Answer:
Personification.
Explanation:
The Soldiers are being personified as chess pieces in the passage. What the commanders are referencing is that they are in an intense battle and have little care or thought for the soldiers.
They are merely the pieces in which the Commanders Strategy is carried out through. The Soldiers have no idea that this is happening.
Optimism can still be present in case something goes wrong with the new world and we have another problem or there are people who just aren't optimistic.
By using the process of elimination, I think the answer is imagery. The author never uses ht words "like" or "as" (simile), or uses repetition of a sound (alliteration), or a sound said like a word (onomatopoeia).
Hope this helped. good luck my dude