How does Fitzgerald demonstrate the ideas of the modernist period in his story?

After World War II, writers attempted to come to terms
with where humanity was going after the belief in many of the things that were held as
fundamental had been shattered.  Disillusioned, many modernists placed their focus upon
individualism, employing a new technique called "stream of consciousness" narration with
the theme of the randomness of life.  Moreover, the Modernist movement was concerned
with the quickening of society towards its destruction and lack of meaning.  Certainly,
several of the elements of Modernism are present in F. Scott Fitzgerald's "Babylon
Revisited."

Randomness of
life

As expatriates in Paris, Charlie Wales
lives a rather hedonistic and impetuous life.  However, with the crash of 1929, things
change drastically for him.  Years later, Charlie does recover financially, but his
personal life is an absolute wreck because of his alcoholism  The fateful night on which
his wife walks in the cold rain is certainly a random act, but one with tragic
results.

Society's movement towards its own
destruction meaninglessness

Charlie Wales
rationalizes his drinking problem and dismisses important issues--"The depression of
yesterday was gone." 

The former friends of Charlie, Duncan
Scaeffer and Lorraine Quarrles seek to "draw a certain sustenance from his strength,"
but they really destroy Charlie's chances of regaining custody of his daughter Honoria. 
Hedonistic, they are only concerned with Charlie's joining them for drinks and
partying.

Constantly Marion, his sister-in-law is the voice
of practicality.  As a foil to Charlie's irresponsibility she often asks such questions
as "Why didn't you think of all this
before?"

Stream-of-consciousness narration
and allusiveness,

In several passages in the
story, Charlie's thoughts are intermixed with the third-person narration, providing the
Modernist stream-of-consciousness, interior monologue.  Here are
examples: 

readability="18">

 He had never eaten at a really cheap restaurant
in Paris. Five-course dinner, four francs fifty, eighteen cents, wine included. For some
odd reason he wished that he had

He believed in character;
he wanted to jump back a whole generation and trust in character again as the eternally
valuable element. Everything else wore out

He would come
back some day; they couldn't make him pay forever. But he wanted his child, and nothing
was much good now, beside that fact.... He was absolutely sure Helen wouldn't have
wanted him to be so
alone.

Individuality

In
his effort to escape the past, Charlie tries to avoid Duncan and Lorraine.  But he
fails, just as he fails to convince Marion that he has changed because he lets his
friends and his alcoholism control him.  Finally, at the end, Charlie engages again in
interior monologue in which he vows to "come back someday"
because

...he
wanted his child, and nothing was much good now, beside that
fact.

Perhaps futilely,
Charlie ultimately understands that he must create his own destiny.  And, so, he
promises not to revisit Babylon the next time.