We don't see much actual warfare until the very end of the movie— what we mostly see in From Here to Eternity is the lives of the soldiers themselves: the way they spend their down time and the way their daily routine is structured. The movie is a detailed study of that life, in many ways.
We see a soldier's life without warfare—the problems of love, the insane difficulties imposed by idiotic officers, the bar-fights and shenanigans—and then we see life with warfare, when the moment of truth comes. Both Warden and Prewitt are defined by the way they respond to this moment, and they both meet it with courage.
Questions About Warfare
How does From Here to Eternity depict the Pearl Harbor attack (i.e. how does the attack change the destinies of the characters, and to what end)?
What would've happened to the characters if America hadn't entered World War II? Take a guess.
How do the different characters react to the outbreak of war? Why do they act differently or similarly? (Think about how Warden, Prewitt, the other soldiers, and the guy guarding the ammunition closet react.)
Chew on This
From Here to Eternity neither approves of nor condemns warfare: it just shows what the lives of soldiers are like in peacetime, and how war ends up affecting those lives.
From Here to Eternity presents an argument for war. If you look at the lives the soldiers were leading before the war, they were sort of unconstructive. But when the war starts, the courage of Warden and Prewitt comes to the forefront—they're able to do what they should be doing instead of suffering comparatively trivial annoyances and problems.