Answer:
The correct answer is:
C) the popularity of Manifest Destiny.
Manifest Destiny was a widely held belief among Americans in the 19th century that the United States was destined to expand its territory across the North American continent. This belief fueled the westward expansion of the United States after the Civil War, leading to the acquisition of new territories such as Alaska and the Hawaiian Islands. It was driven by the idea that the country had a divine mission to spread its values, institutions, and way of life to new territories.