ROMANTICISM. The romance of war leads Henry to enlist in the first place, as it did many soldiers during the Civil War. The supposed glory that would be found in battle was a lure to many young men who thought it was a way to prove their bravery.
REALISM. Crane describes his story in very realistic terms. Blood, wounds, death and dying are all about Henry, and when he sees his comrades shot down before him, the fears he has concerning his own bravery are tested.
SYMBOLISM. One example comes in the form of the Cheery Soldier, who represents a god-like presence who saves Henry in the middle of the night and guides him to safety before disappearing into the darkness.
NATURALISM. Crane's novel is deep-rooted in the naturalistic vein, with a large proportion of the narrative dealing with Henry's inner thoughts and fears. Crane strongly adheres to Emile Zola's doctrine concerning naturalistic fiction:
Zola claims that the naturalist writer should subject believable characters and events to experimental conditions. In other words, take the known (such as a character) and introduce it into the unknown (such as an unfamiliar place).
Henry is placed on the field of battle, where he faces the unknown--both from the actions of the Confederate "dragons" who attack him, as well as from his own personal demons that he must conquer as well.
IMAGISM. Although Imagism primarily was a movement involving poetry, Crane encompasses several of the primary themes: War, sense of place, and nature.
IMPRESSIONISM. Crane's The Red Badge of Courage is an American classic of stream of consciousness impressionism, and the novel is one of the earliest examples of the style. Impressionism in literature
... can basically be defined as when an author centers his story/attention on the character's mental life such as the character's impressions, feelings, sensations, thoughts and emotions, rather than trying to interpret them.
The style allows the reader to decide for himself about the character, giving each reading the possibility of many different interpretations.