Though the war hasn't overtly affected any of the characters in outwardly visible ways, it has affected each one of them by shifting their priorities from the practical to the passionate.  This is most exemplified by Jake and Brett's relationship.  While before the war, young men and women sought for wives and husbands who would be good with money, temperate with children, and patient as spouses, the war forced young people into a mode of feeling starved for passion.  Having lived through the adrenaline-filled years of fighting and having lost so many people in their lives, the war generation began to place supreme importance on living in the moment, leading them to passionate, but unstable, romantic relationships.