Between 1940 and 1970 continued migration transformed the country's African-American population from a predominantly southern, rural group to a northern, rural one. By 1950, the black population comprised approximately 11% of the total U.S. population; in several major cities, black migrants comprised 40% of the population. In addition to their desire to escape the inequities of the Jim Crow South, African-Americans were pulled to Northern cities after 1940 by growing industrialization. This industrialization was fueled after World War II by expanding consumerism and by technologies that quickly made the small farmer obsolete. Such inventions included synthetic fibers as a substitute for cotton and the mechanical cotton picker. With the advent of these and other technologies, sharecroppers were no longer needed on Southern farms. Northern cities promised black farmers relief from political, social and economic oppression, and from constant fear and degradation they experienced in the South. While racism was certainly widespread in the North, wages there were, on average, three times higher than wages in the South; there were no laws enforcing segregation; nor were there literacy tests to prevent blacks from voting. Still, the urban North presented a whole new set of challenges to migrating blacks - from cramped, dilapidated, unsanitary living conditions, to denial from membership in labor unions. In 1910, 80% of African-Americans lived in the South; by 1970, less than half lived in the South, and only one-quarter in the rural South. From 1910 to 1970, in the largest migration in American history, 6.5 million African-Americans left the South.