War- The old lie: Dulce et decorum est pro patria mori "It is sweet and proper to die for ones country". Wilfred Owen was a British WW1 soldier, and wrote the poem while in the trenches.
Grief (Friend/soldier who dies)- If you could hear, at every jolt, the blood come gargling from the froth-corrupted lungs. He grieves the friend who died and wishes he could have helped in some way.
PTSD/Trauma- In all my dreams, before my helpless sight, he plunges at me, guttering, choking, drowning. Shows the impact war had on Owen personally, and that it still impacts him throughout the remaining wartime.