Courage and cowardice
Henry spends the novel trying to figure out what courage is. He runs, lies, then fights recklessly. Crane shows that courage is not a fixed quality — it is tested moment by moment, and Henry keeps failing the test until he stops thinking about it.
Self-deception
Henry is constantly rewriting his own story. He frames his flight as rational survival, his wound as a battle scar, his rage as bravery. Crane's close narration lets readers see through each rationalization even when Henry cannot.
The gap between war's romance and its reality
Henry enlists with visions of ancient heroes. What he finds is mud, confusion, boredom, and grotesque death. The novel systematically destroys every romantic idea Henry brought with him.
Identity and manhood
Henry defines manhood as performing bravely in battle. When he fails, his sense of self collapses. His arc is about rebuilding an identity — though Crane questions whether the rebuilt version is any more honest than the original.
Nature's indifference
Henry looks to nature for moral guidance and finds none. The forest does not judge him. The dead soldier in the clearing is simply rotting. Nature does not care about human courage or cowardice, and that absence of meaning is part of what makes the novel feel modern.