Which natural resource became more available to the American public as a result of railroad expansion?

It was "coal" that became more available to the American public as a result of railroad expansion, because many of the coal mines that were utilized were found in the west and midwest.

Explanation:

the growing interconnectedness of the world through communication, trade, and the exchange of ideas is an important theme in the history of the 20th and 21st centuries.

explanation:

we need the map to answer the question