Answer:
Probably the railroad was the single most important factor that contributed to the American industrial revolution.
The railroad was essential for relocating immigrants, accessing mines in the west and expanding the country in general.
Other important factors include:
Early industrialization increased productivity, and American entrepreneurs realized that and wanted to copy that model. Several American inventions increased productivity.
That led to change from agricultural nation to industrial nation (at least in the northern states).
Businesses expanded and corporations were formed. That led to powerful monopolies.
The government itself did not intervene in the economy that much, it was worried about economic growth and the means were not something to care about.
As more immigrants arrived, markets starters to grow. Also, the government imposed high tariffs on imported goods which benefitted American producers.