What are two possible reasons that the United States became an imperial nation in the late 1800s?

There were many reasons why the United States became an imperial nation in the late nineteenth century. Perhaps the two most important reasons were as follows. 

First, the United States sought markets around the world for its manufactured goods. There was a real fear in the United States and other industrialized nations that the country's economy might fall prey to overproduction--its factories, in other words, might produce more than domestic markets could bear. So American business leaders sought to expand their interests overseas, and pushed the government to adopt policies that protected their rights to trade. The so-called "Open Door" notes, which claimed the right of the United States to trade alongside other nations in China, was an example of this motive in practice. 

Another reason was that many perceived that the United States needed to expand its military influence around the world, especially in the Pacific. This motive went hand in hand with the commercial motives discussed in the preceding paragraph. The United States sought islands in the Pacific as naval bases that could extend its reach into Asia and protect its access to markets in that region. For both of these reasons, the United States emerged as a major imperial power after crushing Spain in the Spanish American War of 1898.