The Chocolate War explores the theme of conformity versus non-conformity and, at its core, the conflict of the book is created by this theme. 

One of the first articulations of this theme comes in Jerry's run-in with the leader of the hippies. The hippies congregate in a park across the street from the school and every day Jerry stands and stares at them in the park, contemplating their decisions as he sees them. 

A hippy approaches him one day and calls Jerry "a square", a conformist who is loyal to the system of rules represented by his school uniform. 

This episode brings the 1960s into focus as a cultural background for the book and identifies the idea of conformity as a part of the cultural context of the Vietnam era wherein the book is set. 

Jerry's later decisions to resist peer pressure and (following the poster in his locker) to choose to "disturb the universe" are grounded in this first run-in with the hippies, their politics and the question of conformity versus non-conformity.