What circumstances bring the wealthy class and the poor class into conflict with each other in The Grapes of Wrath?

I would say that the scarcity of money is what brings the
rich and poor into collision with one another in Steinbeck's work.  The poor
consistently interact with the rich out of anger in the disproportionate nature of
wealth that exists between them.  In the narrative, there is a strict demarcation
between rich and poor and the only time when their worlds collide is over wealth, with
the rich protecting their interests and the poor seeking a share of theirs.  Given the
time period's lack of wealth for anyone, this makes competition particularly brutal and
one where antagonism marks each encounter between both
groups.

I actually think that the land turtle in chapter 3
might be indicative of the struggle between rich and poor.  The poor in Steinbeck's work
seek to continue on their way, struggling through adversity and avoiding contact with
swerving vehicles, in this case representative of the wealthy.  The endless antagonism
over wealth eventually causes one or two cars to hit the turtle and force it on its
shell.  This is representative of the poor's struggle to battle through its formidable
challenges with the rich.  As Steinbeck features the turtle righting itself and
continuing on, so too do the poor find a way to cope and continue on their own path for
happiness.  The symbol of the turtle is representative of the circumstances and
conditions that bring the wealth and poor class into conflict with one
another.

This metaphor is repeated in different settings in
the book.  The "bankers" come to represent one aspect of wealth pressuring the poor,
like the car that swerves to knock the turtle down.  The poor looking for work, only to
find signs that say, "No Help Wanted. No Trespassing" is another example of how the
antagonism between rich and poor exists, or how the land turtle is knocked down by
conditions and circumstances.  Finally, the bosses who seek to exploit the migrants by
offering them "dirt" wages and undermining their efforts again display the dynamic of
the turtle getting knocked over and having to right itself.