In 1904, the NYC subway opened. African American population increased because of the Great Migration from the American South and the Harlem Renaissance. Prohibition was also in effect in New York, and the number of skyscrapers increased. Poverty rates and crime rates ended when immigration was limited and when WWI disputed trade routes. Great Depression ended need for new labor. NYC became the most populated city in the world in 1925. Unionization then ended the mistreatment of industrial workers in NYC. The Harlem Renaissance flourished under the Prohibition Era as well.