The Great Migration is a term used to describe the mass migration of African Americans from the southern United States to the industrial centers of the Northeast and Midwest between the 1910s and 1940s. The Great Migration also initiated the change from a primarily rural to a predominantly urban lifestyle for African Americans. The routes north came to be known as the "chicken bone express," because of the supposed litter left by the migrants from their lunches by the side of the road as they moved.

There are several factors that contributed to this major movement of people within the United States, based on ecology, economics, and racism. They can also be categorized as push and pull factors:

1. A Boll Weevil infestation of the cotton fields of the South in the late 1910s, forced many sharecroppers to search for employment opportunities elsewhere;
2. This was exacerbated by a drop in cotton prices, which meant that landowners could no longer afford to hire outside workers and tenant farmers could no longer afford to pay their rents;
3. World War I effectively put a halt to the flow of European immigrants to the emerging industrial centers Northeast and Midwest, causing shortages of workers in the factories;
4. Anti-immigration legislation after the war similarly resulted in a dire shortage of workers;
5. The Great Mississippi Flood of 1927 and its aftermath displaced hundreds of thousands of African-American farm workers;
6. While they still existed in the North, racial prejudices were less likely to result in severe violence and terror campaigns against the African American population, such as that waged by the newly reemerged Ku Klux Klan;
7. The Great Depression caused people to seek new employment opportunities;
8. Even before America's entry into World War II, industrial production in the Northeast and Midwest increased rapidly as a result of Cash and Carry and the Lend-Lease Act, and people were needed to staff the factories.

The scope of the mass migration is best seen in Detroit, Michigan, a city which, during World War II, earned the title of "Arsenal of Democracy" for its contribution to the war effort. In 1910, the African American population of Detroit was just 6,000, but this jumped to 120,000 by the time of the Stock Market Crash of 1929. Other cities, such as Chicago and New York City also experienced enormous surges in their African American population.

Although there was opposition to the movement of African Americans into cities that were predominantly white (for example, the riots in East Saint Louis, Illinois in 1917 and Detroit in 1943), the Great Migration provided unprecedented economic and educational opportunities for African Americans. Adults were earning higher wages, while children were presented with better educational opportunities. Furthermore, because of war needs and the rising population of African Americans in the industrial centers, in 1943 President Roosevelt's Executive Order 8002, banning racial discrimination in the workplace in all industries involved in the war effort, and paving the way for the civil rights movement.

For the first time in the United States, a significant urban African American population existed and cultural activity flourished, as exemplified by Harlem Renaissance. According to writer Alain Locke, the United States was seeing the birth of the "new Negro."

In the last two decades of the 20th century, a new movement of African Americans within the United States began, and has reached sufficient magnitude to be termed by some as a second Great Migration. Since roughly 1980, large numbers of African Americans have been moving from other parts of the country to the South. These migrants are typically the descendants of those who had left the South in the original Great Migration.

As in the first Great Migration, this movement has been motivated by economic opportunities, this time in booming Southern cities. The primary magnet for the new migrants has been Atlanta, although almost all Southern cities have seen a large influx of native-born African Americans. This movement has been heavily driven by the best-educated African Americans.