How does economic decline correspond to the Joad family's disintegration in The Grapes of Wrath?

In The Grapes of Wrath, the economic situation and the situation of the Joad Family are quite similar in that they both simply deteriorate over the course of the novel. At the beginning of the novel, the family is at least all together and at least has enough in the way of supplies to feed themselves. However, Grampa Joad dies on the first night out on the road, foreshadowing the doomed nature of the Joad family's journey.

By the time the Joad family reaches California, they have suffered another death, as well as two family members abandoning the journey. This hopelessness in regard to the family is coupled with the disillusionment of realizing that California is not the answer to their financial woes, and families are being exploited to the point of starvation. Their family and their finances have withered in equal proportion.

How does economic decline correspond to the Joad family's disintegration in The Grapes of Wrath?

At the start of the journey westward, the Joad family is intact: Grandpa, Grandma, Pa, Ma, Tom, Rose of Sharon and her husband, Noah, Al, Ruthie, and Winfield are all there.  Before they are out of the state of Oklahoma, Grandpa dies.  Soon, Noah decides he doesn't want to leave the river and he stays behind.  Then Grandma dies. Rose of Sharon's husband takes off when he realizes things in California aren't as good as they'd hoped they be. After Jim Casy dies and Tom's injury would identify him as a killer, Tom leaves the family.  Next, Al decides to stay with the Wainwright family and marry Aggie.  The family members left are: Pa, Ma, Rose of Sharon, Ruthie and Winfield. The family is cut in half.  While this disintegration of the family is happening, the family's economic situation which is bad to begin with, declines as well.  When the journey began, the family at least had some food and a truck, but by the time the story ends, they are destitute and have gone into a stranger's barn to try to stay dry because they have no where else to go.  They have no truck, no food, and no money.