Answer the following question: Given the following passage  "Detroit, like many places in the United States, developed racial conflict and discrimination in the 20th century following rapid demographic changes as hundreds of thousands of new workers were attracted to the industrial city; in a short period it became the 4th-largest city in the nation. The Great Migration brought rural blacks from the South; they were outnumbered by southern whites who also migrated to the city. Immigration brought southern and eastern Europeans of Catholic and Jewish faith; these new groups competed with native-born whites for jobs and housing in the booming city. Detroit was one of the major Midwest cities that was a site for the dramatic urban revival of the Ku Klux Klan beginning in 1915. "By the 1920s the city had become a stronghold of the KKK," whose members opposed Catholic and Jewish immigrants, as well as black Americans. The Black Legion, a secret vigilante group, was active in the Detroit area in the 1930s, when one-third of its estimated 20,000 to 30,000 members in Michigan were based in the city. It was defeated after numerous prosecutions following the kidnapping and murder in 1936 of Charles Poole, a Catholic Works Progress Administration organizer. A total of 49 men of the Black Legion were convicted of numerous crimes, with many sentenced to life in prison for murder.",  answer the following question. Note that the answer is present within the text.  Question: What was the Great Migration?
Answer:
hundreds of thousands of new workers were attracted to the industrial city