atticus says that country people, like the Cunninghams, were hit the hardest by " the crash," to what is he reffering ?

The Great Depression was, in large part, a product of the stock market crash of 1929. To kill a Mockingbird reflected the Great Depression era of the 1930's. Country people like the Cunninghams could not afford to grow their crops. Draught also ruined much of what they had to grow so they could not even feed their families.