The correct answer is - African Americans left the south in large numbers to work in war-related industries.
In this period a large portion of the African American population in search of a better life migrated from the south to the north of the country. And since it was a war period, big portion of the jobs available were in the war-related industries, so most of them started working into this facilities to make a living for themselves and their families. This internal migration in the United States caused big changes on regional and local level throughout the country from demographic point of view.
U.S. factory owners and employment agencies had begun recruiting heavily on Puerto Rico.
After 1945, economic changes transformed Puerto Rico's economy from a monocultural plantation economy into a platform for export-production in factories through what was called Operation Bootstrap. By the 1950s a growing unemployment problem left thousands of Puerto Ricans in need of a fresh start on American companies.
