The massive stream of European emigration to the United States, which had begun in the late 19th century and waned during World War I, slowed to a trickle with immigration reform in the 1920s. As a result, urban industries were faced with labour shortages. A huge internal population shift among African Americans addressed these shortfalls, particularly during the World Wars, when defense industries required more unskilled labour. Although the Great Migration slowed during the Great Depression, it surged again after World War II, when rates of migration were high for several decades.
