There have been several times throughout the story so far where the war has been mentioned. Since the novel is set in the 1920s of Paris, this war previously referred to must be World War I. In my opinion, the war is probably to blame for everyone's prejudice and preconceived notions about others. I've picked up that certain nationalities were mistreated at this time (i.e. Cohn for being Jewish, Georgette mentioning that she hates Flamands). Either way, the war's affect on society intrigues me. It also revealed more about Brett.
"I don't know. I just don't believe it. Have you known her a long time?" [Cohn]
"Yes," I said. "She was a V.A.D. in a hospital I was in during the war." [Jake] (page 46)
This must have been how Jake and Brett met one another. It made me sad to hear that her one true love died of dysentery. All in all, I think that Hemingway's allusion to the war is an important one for the reader to better understand the time period.