Which war is the setting for Ernest Hemingway's book, "A Farewell To Arms"?

Ernest Hemingway is accurate, right down to the weather (which is very important to the story); thus, it doesn’t take too much research here to pin down the setting. And, when we read that Catherine’s fiancé died the year before, we can look up the Battle of Somme and learn that it must be 1917. Also, when we read about the Italian retreat from Caporetto, we can look it up and confirm that it is 1917 and World War I.

There is no doubt or confusion that Ernest Hemingway's book, "A Farewell To Arms" is taking place during World War I. We find that in Italy in World War I it is a fractured and broken landscape, which mirrors the tragic and breaking lives of the characters. The only safe places are bedrooms, bars, and hospitals, and even the seemingly safest settings in this novel are suffused with fragility.

Thus, this novel which was published in 1929 is a first person account of American Frederic Henry, serving as a Lieutenant in the ambulance corps of the Italian Army.