Final answer:
Cornelius Vanderbilt controlled most of the important railroad lines in the United States by consolidating smaller lines into the New York Central Railroad Company.
Step-by-step explanation:
The individual who controlled most of the important railroad lines in the United States was Cornelius Vanderbilt. He played a significant role in the consolidation of several smaller railroad companies into what became the New York Central Railroad Company, thereby creating one of the largest and most powerful corporations in America during that era.
Vanderbilt’s influence on the railroad industry was part of a larger movement of industrial contributions by several entrepreneurs known as "robber barons." These figures, including Andrew Carnegie, John D. Rockefeller, and J.P. Morgan, greatly influenced the country through their business strategies and control over key industries like steel, oil, and finance, respectively. However, when it comes to the control of railroad lines specifically, Vanderbilt stands out for his contributions to creating an efficient network that connected the Midwest to the East.
Cornelius Vanderbilt’s model of railroad consolidation differed from that of others like Jay Gould, who also amassed a significant portion of railroad control but focused more on financial profit than on the tangible improvements within the network. While J.P. Morgan did control the finances of numerous railroads, it was Vanderbilt who is known for directly controlling the rail lines.