The Red Badge of Courage is a novel about the Civil War, and is probably the modern Trope Codifier for War Is Hell. The book is about Henry Fleming, a young soldier of 304th regiment who flees a battle, but eventually returns to win the day.
This book provides examples of:
0% Approval Rating: The rating the 304th Regiment gave to their commanding officer after he calls the entire regiment "mud diggers".
The American Civil War: Based canonically (according to the sequel, The Veteran) on the Battle of Chancellorsville.
Do Not Do This Cool Thing: Averted, since there is very little warfare actually shown; Henry is fleeing for much of it, and in the end he becomes a man because he doesn't want to fight any more.
Grey and Gray Morality: The novel avoids discussing which side is right. Just that both sides are fighting. Stephen Crane goes even a step further and just call the Unions "blue" and Confederates "gray", except in dialogues such as when the cheerful soldier led Henry back to 304th regiment and called the Confederates "Johnnies", a derogatory slang at that time towards the Confederates.
Heroic Sacrifice: Henry have the romantic notion of this at the beginning of the novel.
In The Veteran, Old Henry tries to save the two old colts at the end of a burning barn. The roof collapse before he would've gotten out.
Infant Immortality: Subverted, being realism and all. More than half of the 304th Regiment died in the final battle.
It rained. The procession of weary soldiers became a bedraggled train, despondent and muttering, marching with churning effort in a trough of liquid brown mud under a low, wretched sky. Yet the youth smiled, for he saw that the world was a world for him, though many discovered it to be made of oaths and walking sticks. He had rid himself of the red sickness of battle. The sultry nightmare was in the past. He had been an animal blistered and sweating in the heat and pain of war. He turned now with a lover's thirst to images of tranquil skies, fresh meadows, cool brooks—an existence of soft and eternal peace.
Rule of Symbolism: Many things symbolize that nature does not care about humanity, such as:
the decaying body of an Union soldier Henry found when he runs away
Tattered Flag: In the movie adaption, Henry charged with the tattered Union flag. He captured the Dixie in the end, more tattered than the Union flag.
Title Drop: The title refers to an injury suffered in battle, though in Henry's case it was actually delivered by a panicking soldier from his own side who he was trying to dissuade from running after overcoming his own fear of battle.