How does Salinger use the past event of Holden witnessing his old friend, James Castle, committing suicide to affect the novel as a whole?
In Salinger's novel of teen angst, the sensitive, perceptive, and intelligent Holden Caulfield, who becomes cynical, finds himself teetering between the innocence and naivete of childhood and the disillusionment of adulthood. Moreover, death haunts Holden ever since the loss of his sibling; he fears connecting with people, perceives both teens and adults as "phonies," and searches for meaning in the world of distortion in which he finds himself.
It seems important to consider Catcher in the Rye in its historical context because Salinger hints at the repercussions of the atomic bomb in the preoccupation that Holden has with death, in his perceptions of people as "phonies," and the general meaningless that he feels life has. As a matter of note, his sibling Allie has died of leukemia, the disease from which many survivors of the atomic bomb died. Certainly, her death and the death of his friend James Castle has a profound effect upon Holden.
And, it is this senseless death of James that extends to the senselessness of so many deaths in the world in which Holden Caulfield finds himself fearful of life and disillusioned with adults. In Chapter 22, when Holden sneaks into his little sister's room to talk with her and to be in the midst of innocence--he even mentions "innocent guys" to Phoebe as he says lawyer are all right if they defend such people--the memory of James Castle haunts him as symbolic of the cruel death of an innocent, just as there were many horrific killings of innocence in World War II. Holden's description of James Castle lying of the stone steps of the dormitory could easily be that of one killed in the war:
He was dead, and his teeth, and blood, were all over the place, and nobody would even go near him.
In his struggle to reconcile in his mind the senseless death of innocents such as Allie and James, Holden becomes obsessed with the idea of death and the seemingly meaninglessness of so many "phony" lives.