This question is asking how the title of the novel, The Chocolate War, relates to the action in the book; a good question but one without a single answer.
The action of the novel centers on a chocolate sale at Trinity High School, a public, Catholic all-boys school. Students at the school are expected to sell fifty boxes of chocolate in a fundraiser but one student, Jerry Renault, refuses to sell the chocolates.
Jerry is influenced in his decision by a secret group of students in the school, the Vigils, who function as a powerful syndicate within Trinity. The Vigils tell Jerry not to sell any chocolates and he goes along with the command, but when they tell him to start selling chocolates later Jerry refuses.
This is a chocolate conflict.
The conflict, arguably, rises to the nature of war when Jerry becomes a casualty. At the end of the novel, though he does not die, Jerry is seriously beaten and sustains injuries as a result of his refusal to give in to the Vigils and to school authorities.