How does Gatsby represent the American dream? What does The Great Gatsby have to say about the condition of the American dream in 1920s ?

I think that
one of the majorof the novel is that the American dream has lost its purity.  The author is
using the book to argue that the pure American dream of improving yourself has been lost and
what they now have is a soul-less pursuit of wealth.

represents this process
because his story is supposed to be the American dream -- he rises from poverty to become rich
and famous.  But the way he has done it and his reasons for doing it are not pure at all.  He
has risen by crime, not by hard (legal) work.  And he is not doing it for a good purpose but
rather to get the love of a woman who cares only about money.

Fitzgerald saw
the '20s as a "lost" time in the US.  He thought people were shallow and
materialistic.  You can see that idea in this book.