By 1860, the number of miles of railroad tracks throughout the united states had risen to
a.3,000.
b.30,000.
c.300,000.
d.3 million.

Contributing factors  leading  to the harlem renaissance were the great migration of african americans to northern cities, which concentratedambitious  people in places where they could encourage each  other, and the first world war, which had created new industrial work opportunities for tens of thousands of people.