Do We Have To Be "American" to Be American?

A question brought up quite often recently in English class due to our task of defining American Literature is, does an author have to be from America to be an American author and therefore qualify their literature as American Literature? I took this question and changed it to better my curiosity by asking, do the characters in a book have to be from America to qualify a book as American Literature, even if the author is American themselves? This question came up because in the book The Sun Also Rises by Ernest Hemingway, all the characters are traveling or living in countries outside of America such as Paris, South America, Spain, Scotland, and Greece. The difference that is made in this storyline is that all the characters are united through their involvement in World War I, the majority of them having fought in the war for America. Even the female character Brett is involved through her work in the hospitals of the war and other characters are friends of war veterans. The setting of the book however is not America and the characters are obviously expatriates. Therefore, can the book still be categorized as an American piece of literature or do the characters and plot of the story have nothing to do with the book's qualification in such a category?

I believe that the author's own status as American is a large factor. The author himself being from America and having knowledge about World War I and its effects evident in the characters who are said to have been present shown through his descriptions of them contribute to the books American genre. I also think that the since the main characters in The Sun Also Rises were all united by the same conflict in America, their efforts in World War I, that even if they're lives take them elsewhere in the world they have the American background and the American identities that are needed. Therefore I do think that we have the characters had to be American in order for the book to be a piece of American literature, but they do not have to spend their entire lives in America as long as they know where they came from and that background affects them and is evident in their actions and beliefs wherever they do go.