What distinction does Steinbeck draw between causes and results?

In Chapter 14 Steinbeck describes how the trickle of farmers from Oklahoma and the Midwest has become a deluge of the desperate and the dispossessed. Ditches have become settlements. People in the west are scared of what they perceive as the hordes at their doorstep. Largely through subtext, Steinbeck poses the question of cause and effect. Was it the draught that caused such suffering or was it the callous reactions of the capitalist system? When desperate hungry people are not helped by their own government and fellow citizens, is not a revolt the logical effect?