Question

it was during the first world war that a silent pilgrimage took its first steps within the borders of this country...it would not end until the 1970s...over the course of six decades, some six million black southerners left the land of their forefathers and fanned out across the country for an uncertain existence in nearly every other corner of america... - isabel wilkerson, the warmth of other suns: the epic story of americas great migration, 2010
what was a primary reason for the demographic shift described in this excerpt?
increased demand for sharecroppers in the north
a lack of educational institutions for african americans in the south
increased availability of manufactured goods in the north
limited economic opportunities for african americans in the south

Explanation:

The Great Migration of Black Southerners was mainly driven by limited economic opportunities in the South. Sharecropping (not increased demand for it in the North) was a restrictive economic system in the South. Lack of educational institutions was a factor but economic pull - push (more jobs in the North, limited in the South) was primary. Availability of manufactured goods was not the main driver. Economic opportunities (or lack thereof) were key.

Answer:

Limited economic opportunities for African Americans in the South.