Final answer:
The completed railroad boosted Washington Territory's economy by transporting mineral resources and facilitating the movement of people, which contributed to the industrial expansion and urbanization. It also provided stability and connectivity, fostering a national market system.
Step-by-step explanation:
The completed railroad significantly boosted the economic development in the Washington Territory in two main ways. First, it facilitated the transport of the vast mineral resources found in the western states, which were essential for the nation's industrial expansion.
This made the exploitation and shipping of materials like coal, iron, and timber much more efficient, contributing to the growth of industries such as steel manufacturing. Second, the railroad played a critical role in shaping demographic changes by encouraging the movement of people, which included an influx of fourteen million immigrants who provided labor for factories and helped to transform the United States from a rural country to one with vibrant urban centers.
Railroads also provided stability and connectivity to the growing nation, which was essential for effective governance across vast lands. They underpinned the creation of a national market system, promoting economic integration and the expansion of domestic and international markets.