Final answer:
Americans were motivated to build the Transcontinental Railroad to connect East and West, spur economic growth, and establish a unified national transportation and communication network, signified by the driving of the golden spike.
Step-by-step explanation:
The construction of the Transcontinental Railroad was driven by several key motivations. First, the desire to connect the East with the promising lands of the West for both settlement and commerce was a major factor. With the railroad in place, it would be easier to transport goods and people across the vast distances of the nation. Secondly, there was an economic incentive; the railroad would provide a boost to industries such as iron, wood, and coal, fueling economic growth. The federal government saw the potential for land along the railroad to gain in value which would, in turn, create revenue from land sales. Lastly, the railroad was seen as a way to provide quicker and more reliable communication and transportation across the country, thus helping to govern an ever-expanding country. This was facilitated by the related growth of the telegraph system alongside the rail network. On May 10th, 1869, when the golden spike was driven at Promontory, Utah, it marked the completion of a monumental engineering feat that physically united the nation and became a catalyst for further industrial and economic transformations.