Answer:
labor for industries.
Step-by-step 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.