Final answer:
Cornelius Vanderbilt invested his fortune in railroad expansion, creating the New York Central Railroad Company and enhancing the efficiency of transportation networks in the US.
Step-by-step explanation:
Commodore Cornelius Vanderbilt invested his fortune into railroad expansion after selling his previous holdings. Known as a "robber baron," Vanderbilt significantly influenced the American economy through his involvement in the railroad industry. He consolidated several smaller railroad lines to create the powerful New York Central Railroad Company, which became one of the United States' largest corporations. Moreover, Vanderbilt's actions led to more efficient connections between Midwestern suppliers and eastern markets by creating a solid railroad network from Chicago to New York City.