Final answer:
Statement 3 is correct, indicating that railroads post-Civil War encouraged urbanization, western settlement, and a national market, and fundamentally shaped American society and its economy.
Step-by-step explanation:
The statement that accurately describes how Americans were influenced by the growth of railroads after the Civil War is Statement 3: Railroads encouraged the growth of cities, settlement of the West, and creation of a national market.
The development and expansion of the railroads after the Civil War not only transformed transportation and the economy, but they also initiated the transition from rural areas to urban centers, fueled the immigration of workers into factories, and supported America's industrial expansion.
Railroads also played a crucial role in the settlement and agricultural development of the West, contributing to America's emergence as a national market.