Final answer:
The growth of the railroads post-Civil War is indeed true to have helped America become the first mass-manufacturing nation by providing efficient transport for resources and goods, pioneering technological advancements, and facilitating urbanization and economic growth.
Step-by-step explanation:
The statement that the westward growth of the railroads helped America to become the first mass-manufacturing nation is true. The expansion of the rail network post-Civil War played a critical role in America's industrial revolution. Railroads not only facilitated the efficient transport of raw materials like minerals from the Western states but also connected manufacturers to national markets. The introduction of the transcontinental railroad and the technological advances in steel manufacturing led to more robust and expansive rail infrastructure, capable of supporting the transportation of heavy loads across the country.
With the railroads providing an effective distribution network, industries such as steel, textiles, and armaments flourished. Innovations like the telephone and the electric light bulb emerged, further advancing America's economic status. The railroad boom also contributed to urbanization as people migrated to cities for factory jobs, transforming America from a predominantly rural nation to an urban mass-manufacturing powerhouse. This shift significantly increased the population and economic size of the country, laying the groundwork for America's status as a leading industrial nation.