You have picked two poems that present very different perspectives on war and patriotism. Briefly here are a few points to get you started which you will need to develop to answer the question fully.
"The Soldier" has a lyrical, lofty tone, fitting its idealistic attitude to war and patriotism. It is very interesting to compare how the death of soldiers is viewed in this poem as compared with "Dulce et decorum est" - here the death of a soldier is going to propogate the British empire - "some corner that will be forever England". Here the individual is clearly positioned under the country and shows itself to be glad to give up his life in honour to defend the idea of what England represents to him. It is clearly patriotic, jingoistic and presents a very romantic approach to war and death in general.
"Dulce et decorum est" is completely different, written in response to sentiments like those expressed in "The Soldier", presenting us with a grim scene of the reality of life for soldiers during the war. You will want to examine how the soldiers are described in ways that dehumanise them ("bent over", "coughing like hags", "drunk with fatigue") and the way the gas attack, and in particular the death, is described. There is nothing glorious about war, nothing fine about death, which is horrid, lingering and brutal. You will also want to consider the way the poem changes its tense and person - finally, accusingly addressing the reader in the last paragraph.
Lots more to say, but that should get you started!