What makes West Side Story a tragic play?

Aristotle defined tragedy in the Poetics as an action performed by actors (not narrated) that has three parts (an introduction, middle, and ending). In addition, he defined tragedy as providing catharsis, or the purification of the emotions, as the audience watches action that moves them to pity or fear. West Side Story has all of these elements of a tragedy. It has a beginning (when Tony and Maria meet); a middle (when Tony and Maria are together); and a sad end (when Tony dies). The action is performed by actors, and Tony and Maria's experiences, including their reactions to Bernardo's death, their unmet hope to be together in a peaceful place, and Tony's death, provoke strong emotions in the audience. In the end, the audience experiences a catharsis, or a purification of the emotions, after watching the play.