How did The Great Gatsby come to be considered such an important piece of literature?

Between initial publication in 1925 and the second world war only twenty thousand copies have been sold. Then one hundred fifty-five thousand copies were distributed to American soldiers. That book owes it's importanc to the fact it's been one of the novels picked up by the Amercian «Council on Books in Wartime».

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Which in turn might have been influenced by the death of Fitzgerald in December 1940.