Many immigrants moved to the united states in the late 1800s to
work in technical industries.
form megalopolises.
build the railroads.
live in the sunbelt states.

work in technical industries

Explanation:

During the late 1800's the industry in the United States was booming, and with the rate it was growing it needed more and more labor force. This attracted lot of people from abroad to immigrate toward the United States, as they had ensured jobs and were going to work in the technical industries. The people were encouraged and optimistic moving in the United States, stop working in agriculture and start a new life in new country, working int he industry, and living in a city instead of rural areas.

because the center-south is called the heart of the country