Which of these industries made america's first millionaire.
a. the steel industry
b. the banking industry
c. the railroad industry

The railroads led to the first millionaires in the US. During the days of railroad production, entrepreneurs would enlist low-cost immigrant labor to lay miles and miles of track, leading to the first hyper-wealthy people in US history. In this industry, it was profitable to be able to procure the track and use whatever means possible to get as much of it placed in as little time as necessary.