How O'Brien highlights the difference between the "real world" and the "safe world".

Throughout the story O'Brien draws a line between the "real world" and the "safe world". The real world being Jimmy's world, the war, where men are die everyday, where the people live under extreme conditions, where life itself becomes a burden sometimes and needs to be carried by the men. The safe world being Martha's world, where they care about literature, have no danger to life, enjoy with friends, and live life to fulfill their dreams.
O'Brien compares the life of the people in both the worlds and shows the significant different. This is done mainly through the comparison of the life of Jimmy Cross and that of Martha. Even though the story is mainly about Jimmy's realization, it can be seen that a difference is established by the end of the story. Jimmy Cross even talks about the difference. "...she belonged elsewhere. He would shut down the daydreams. This was not Mount Sebastian, it was another world, where there were no pretty poems or midterm exams, a place where men died because of carelessness or gross stupidity"(O'Brien 383). This sentence is one of examples given by other to outline the two separate worlds.
Jimmy Cross lives in a world of pistols, machine guns, grenades, tanks, jet fighters, etc. and Martha lived in a world of poetry, shopping, beaches, parties, movies, etc.
The moments where Jimmy Cross escapes from reality are the moments where the differences can be noticed and these moments usually came after a description of their weapons was given. It can be noticed that by putting the story in such a format the author is actually trying to establish somewhat of a boundary between the two worlds. This pattern is followed till the second last page of the story where the story changes to a somewhat different format to describe the ending of the story.