Which historical event most caused the US urban population to climb from 6 million to 44 million between 1860 and 1910?

The Development of Factories during the Industrial Revolution

Explanation:

Hope this Helos

it was on the rise and doing very well and would continue to do well until the great depression from 1929-1939

on the morning of  july 21,  1861, general mcdowell ordered the  unionarmy to attack. it was on this hill that  confederate  colonel thomas jackson and his forces held back theunion  troops.