Final answer:
The Eastern time zone had the largest concentration of railways in 1890, driven by industrialization and population and crucial to the nation's economic growth.
Step-by-step explanation:
In 1890, the time zone with the largest concentration of railways in the United States was the Eastern time zone. This was a period of rapid expansion for the railway network after the Civil War, with the government offering land grants and low interest loans to support development. The Eastern time zone was the most developed part of the country in terms of industrialization and population, both crucial factors for railway expansion. By connecting various cities and enabling the transportation of goods and people, the railways significantly contributed to the economic growth of the nation. The adoption of standard time zones was also driven by the need to coordinate the complex schedules of the railway system, a change that made interstate business and travel more manageable.