Until the 1900s immigration to the United States was fairly simple because of the need for...

labor for industries.

Explanation:

The 19th century in U.S saw massive industrialization all over the country. It led to a massive need of workforce and labor to work on these industries. At the same time, new cities started to grow in the country with industrialization and urbanization.

To meet the demands of the new cities, industries started manufacturing more steel, iron, textiles, etc. which all consequently led to the need of more workers and labors in the country.

Dcalifornia they have the most people with 200+ people per square mile

Urban growth invariably feeds increased commercialization and industrialization. it requires continually expanding land areas. when urbanization rates are high, and countries do not have the institutional and managerial capacities or economic wherewithal to manage such rapid growths, they exert intense pressure on the types and nature of the resulting settlements. they contribute to the development of overcrowded slums and shanty towns without adequate essential services and necessary infrastructure.-by asit k. biswas and cecilia tortajada