After the first world war started in 1914, industrialized cities in the North, Midwest, and West were faced with a shortage of industrial workers. As war production began to kick into a higher gear and the U.S. entered "total war", Northern recruiters convinced African-Americans from the South to migrate North. At the start of 1920, approximately 1 million blacks had already left the South.
From 1910 to 1920, the black population increased in many of the Northern cities. For instance, New York increased by 66%, Chicago increased by 148%, Philadelphia increased by 500%, and Detroit increased by 61%. Many of these African-American migrants found jobs in factories and slaughterhouses. While segregation was not legalized in the North, as it was in the South, the blacks still faced harsh treatment and racism. It soon became tough for African-Americans to find jobs although they were recruited, some of the Northern factory owners did not want them up North.
1919 became the greatest period of interracial strife in U.S. history, including a disturbing wave of race riots. The most serious took place in Chicago in July 1919; it lasted 13 days and left 38 people dead, 537 injured and 1,000 black families without homes.
The Great Migration had a lasting effect on African-American culture, as many blacks decided to create their own cities within larger urban areas. The most prominent example of this was in Harlem, which was an in formerly all-white neighborhood that by the 1920s housed some 200,000 blacks. The black experience during the Great Migration became an important theme in the artistic movement known first as the "New Negro Movement" and later as the Harlem Renaissance, which would have an enormous impact on the culture of the era.
When the U.S. sank into the Great Depression, the Great Migration slowed greatly. However, by 1970, when the Great Migration "officially" ended, less than 50%of the African-Americans in the U.S. lived in the South.