As with most migrations, there were several factors that drew African Americans out of the South and into cities throughout the nation. Poverty, the lack of educational facilities for the children, rigid segregation and discrimination, and limited opportunities were all among the reasons that led some to look North.

The Negro Leaves the South from Demography, vol. 1, no. 1 (1964) by C. Horace Hamilton

But the most important was the massive collapse of Southern agricultural employment. The principal factors contributing to this economic disaster were great declines in the prices of sugar, tobacco, and especially cotton, coupled with the negative effects of federal policies designed to rescue Southern planters (at the expense of the workers) and the restructuring of commodity production that followed.

With the onset of the worldwide depression, cotton prices fell from 18 cents a pound in 1928 to less than 6 cents a pound in 1931. Despite crashing prices, demand was suppressed further by continued high production that bloated surpluses; in the face of the price collapse, farmers harvested a record crop in 1933. Cutting production seemed to be the only solution. The Roosevelt administration achieved this by paying farmers to reduce the land planted and by buying up surpluses already on the market. Although the U.S. Supreme Court declared the initial program, the Agricultural Adjustment Act, unconstitutional, a revised system was put into place during the late 1930s and achieved the same ends.

Farm owners now received direct subsidies for taking land out of production, as well as so-called parity payments that reimbursed the difference between the actual cost of production and the market price of their product. The owner's tenants and sharecroppers were to share in the benefits of crop reduction. In practice, however, most tenants and croppers were excluded from most, if not all, of these subsidies.

In addition, the New Deal's reduction in acres planted meant that fewer workers were needed to make a crop. This initial reduction was made even worse by mechanization. For the longest time, Southern planters - in control of a captive, cheap, and intimidated labor pool - had little reason to mechanize; but now, with subsidies providing the capital and parity payments guaranteeing a profit, they began to use tractors. Although labor needs ballooned at harvest time, they could be met by turning former tenants and croppers into temporary wageworkers.

Between 1930 and 1950, the number of Southern tenant farmers was cut roughly in half, while the number of tractors tripled from 1940 to 1950. A Mississippian, Maud Jones, recalled those days: "It seemed like all the jobs that came through then, the white had them all and there wasn't anything for the black people to do but still go back to the field. They didn't go to school to cook for a tractor driver, so they just didn't stay here to do it."

Adding to the problems, many planters began to use the mechanized cotton picker. The need for laborers at harvest time was thus drastically reduced. One displaced cropper, Mae Bertha Carter, remembered, "I didn't stay on the farm too long after that. When those mechanical cotton pickers came in was about the time we were told to leave the farm." A social organization of production - the sharecropping and tenant system - that was almost a century old was eliminated. By 1940, moreover, the United States was no longer producing the majority of the world's cotton, and by the 1950s, the South was no longer the dominant source of cotton even within the United States. For many Southerners, it was time to go.

Legendary blues singer Koko Taylor grew up chopping cotton in the Mississippi Delta. She was one of the many thousands who didn't stay:

When I was 18 years old, I left Memphis, my husband and I. And we got the Greyhound bus up Highway 61 and headed north to Chicago. He didn't have no money and I didn't have no money. We had one box of Ritz crackers that we split between us. With no money, nowhere to live, no nothing; we was just taking a chance. And I figured, "If he got enough nerve to take a chance with nothin', I have too." So that's what we did.