How does the author convey his theme in The Red Badge of Courage?

While The Red Badge of Courage has more than one theme, or message, that Stephen Crane proposes through his narrative, the Naturalistic theme seems the most salient.  That is, Crane portrays Nature as an impersonal force with Henry Fleming isolated and alone.  For, as a man, Henry is at the mercy of a superior and cosmic force in spite of his own thoughts and instincts.

Here are two examples of this theme:

1.  Stephen Crane candidly reports the inhumanity of man to man amid the brutish forces of nature.  When Henry runs from the violence and chaos, he finds no solace in the woods; instead, he is

obliged to force his way with much noise.  The creepers, catching against his legs, cried out harshly as their sprays were torn from the barks of trees. 

As he moves deeper into the woods, he espies what he believes is a lovely spot only to happen upon the horror of discovering a decaying body.  As he flees, Henry turns, fearing that the corpse may be calling out to him:

Off was the rumble of death.  It seemed now that Nature had no ears....He conceived Nature to be like a woman with a deep averson to tragedy.

2.  At the very end of the novel, after Henry has suffered through his fears and isolation and emerged triumphant from battle, the weather of the indifferent nature is similar to that of the battle in which he has run away. In Chaper VII, Crane describes the setting:

At length he reached a place where the high, arching boughs made a chapel.  He solftly pushed the green doors aside and entered.  Pine needles were a gentle brown carpet.  There was a religious half light.

But, in the next sentence Crane narrates,

Near the threshold he stopped, horor-stricken at the sight of a thing. He was being looked at by a dead man who was seated with his back against a columnlike tree.

This gruesome sight is placed amid the tranquil beauty of nature in much the same design as that of the novel's conclusion which portrays Henry's victory and coming of age, rather than his frightened fright, evincing the indifference of Nature to that which transpires with man, although Henry imagines that it is sympathetic as he has "rid himself of the red sickness of battle,"

with a lover's thirst to images of tranquil skies, fresh meadows, cool brooks--an existence of soft and eternal peace. 

How does Stephen Crane present themes of loss and recovery in The Red Badge of Courage?

Stephen Crane's The Red Badge of Courage is a story of war. It deals heavily with loss, but the novel also finds a sense of recovery by the end. Let's look at how that works.

The story's protagonist is a young soldier, Henry Fleming. As the novel opens, he is about to enter into his first battle. He quickly begins to feel helpless—it is as if the regiment has enclosed him and he is being pushed along by events outside his control. He begins to lose himself in the midst of the regiment, becoming “not a man but a member.” As the enemy charges, the regiment begins to break and run, and Henry follows suit.

Henry runs wildly from this fearful situation. Later he must deal with that act, which he identifies as cowardly. He has lost his courage, and he needs to account for it. He tries first to justify running as the most intelligent thing to do, but then he learns that most of the regiment actually turned and held. Henry's guilt returns, and he tries to blame his fellow soldiers for not running with him. He has lost his connection to them, even thinking of them as enemies.

As the novel progresses, Henry meets various types of soldiers, speaking to them and losing them as he continues his journey. In the end, Henry returns to the regiment and fights; he becomes quite aggressive and leads his fellow soldiers into battle. He recovers his courage, yet Henry refuses to become overly proud about it as he remembers his past actions. He even takes up the regimental flag after the color sergeant dies. Henry has learned that war is not what he thought it would be and come to terms with what it truly is.