If we see the novel as a dramatizing of a love affair beset by the shifting realities of war, we can identify the novel as a commentary on a cultural change from a world where people were capable of being together peacefully to one where love is a fatal enterprise.
Frederic and Catherine only want to live, together, in love and this proves impossible.
The glory and the heroism that one would share in the experiences of World War I was pure illusion for most. In his novel All Quiet on the Western Front, which is also set during World War I, Erich Maria Remarque describes with excruciating detail how a young man's world of duty, culture, and progresses is bombed away in the trenches along with his countrymen.
Those who fought in World War I were struck with the meaningless slaughter of lives, the unreasoning hatred that pit young men of the same generation but of different uniforms against one another.
As one of the "Lost Generation," Hemingway and his contemporaries were disillusioned and guilt-ridden after the carnage and senseless deaths of millions.
World War I was demoralizing and destabilizing for the western world. The 19th century had been a time of growth and expansion for the countries of Europe and for the U.S. New advancements in science and technology had shrunk the world, improved life span and life quality, and led to greater literacy and education the world wide. People felt in control. World War I obilerated this feeling. The technology that had been so praised led to indescribable horrors on the battlefield, and more single day deaths than in any previous war. The reasons for war were badly understood and morale for the fight was low. Henry "farewell to arms" demonstrates this; he has no invested interest in fighting and leaves - risking arrest and imprisonment - to pursue his own goals. After WWI, this need to pursue personal freedom and goals will dominate. Hemingway and his contemporaries - the expatriates - are living proof, deserting their own country in protest of the cultural concerns.