The correct answer is 3. An increase in urbanization
Explanation
The industrial development of the United States of the nineteenth century was stimulated by the construction of the railroads, which began in 1830 and accelerated from 1840. In the period 1840 - 1860, industrialization was based, above all, on the production of consumer goods, first of all, that of cotton textiles, followed by footwear and leather, iron and machines.
This increase in production made urban areas grow considerably because the people who lived in rural areas moved to the cities, where they found good employment opportunities in the industrial factories of that time, also, most immigrants settled in the cities and therefore urbanization occurred as an effect of industrialization. So, the correct answer is 3. An increase in urbanization
