L.A Question

The question: Ernest Hemingway's experiences in World War 1 changed him forever. How did those experiences affect his writing?
Ernest Hemingway was a volunteer ambulance driver. He was injured by shrapnel from a bomb, and was sent home. He probably saw horrible things that he could never forget. This affected his writing by making it less happy and more (from my point of view) hopeless. By that I don't mean that he was a bad writer, he was quite famous, but I mean that of the stories that I've read (one), they do not have victorious endings, but instead, endings with defeat. Although that's not really the way to describe it either, because as Santiago says in "The Old Man and the Sea", "Man was not made for defeat. You can destroy a man, but not defeat him." I guess his writing is more about not trying to do more than you can handle, and that you need pride, but you can't live with it either.
Many people remember Hemingway being happier and funnier before the war, but, as war often does, he lost his sense of humor and hapiness after seeing all those horrible things. I think that if Hemingway had not been in the war, his novels would end in victory and he might have a bit of humor here and there as well.