Question

a new industrial age & the immigration boom
what was the largest industry in the united states in the late 1800s?
a union for railway workers
the railroad was the number one industry in the united states in the late 1800s. with the growth and expansion of railways across the country, there were enough railroad workers to form their own union.

• the american railway union (aru) was formed and limited to only railway workers.
• the first major strike, the great strike of 1877, involved railway workers and the railroad industry.

steel industry
railroad industry
oil industry

Explanation:

The text clearly states that the railroad was the number - one industry in the United States in the late 1800s. It mentions the growth and expansion of railways and the formation of a union for railway workers, indicating its prominence.

Answer:

railroad industry