Nick was referring to the discovery of George's body. Holocaust is defined as a slaughter...... Myrtle, Gatsby, and Tom had each lost their lives for nothing....... they were the sacrifice of those who didn't care for anything or anyone beyond themselves.
Hope this helps!
The irony in these excerpts from “In Another Country” by Ernest Hemingway convey that the war is ruthless and took away the things most important to the identity and happiness of both men. It also clearly shows that the soldiers had completely lost their identities and expectations.