What explains the United States rise to the industrial and economic importance in the late nineteenth century?

the railroad industry led to the development of other processes.

Explanation:

Having refrigerated train cars allowed meats to distributed throughout America, allowing the agricultural economy to benefit, ultimately enabling the US to profit. It also created a whole new industry, creating more jobs in certain cities. Those cities had to create housing etc to accommodate the influx of people coming in for jobs.

b. native americans them

the second significant cause of the great migration was the desire of black southerners to escape segregation, known euphemistically as jim crow. rural african american southerners believed that segregation - and racism and prejudice against blacks - was significantly less intense in the north.