Answer:
Gradual urbanization and industrialization
Explanation:
In the United States, from 1800 to 1900, the process of urbanization was active: the share of urban population increased by more than 5 times (from less than 10 to 55%). The population of New York was growing at an unprecedented pace. Over the specified period, it increased by 80 times. The development of industrialization and high scientific and technological progress have led to a huge influx of urban population. The number of immigrants and workers from rural areas increased. Industrialization and urbanization reinforced each other.