- Coal was essential for powering steam engines, which were used to drive machinery in factories, mills, and transportation systems. The United States had abundant coal reserves, particularly in the Appalachian Mountains and the Midwest.
- Iron ore was essential for the production of steel, which was used in the construction of railroads, bridges, buildings, and ships. The United States had rich iron ore deposits in the Great Lakes region, particularly in the Marquette Range of Michigan and the Mesabi Range of Minnesota.