Why did the U.S. become an imperial power in the late 19th century?Imperial power - how best to define it...
This is open to historical interpretation, of course, but the short answer is financial gain, emerging nationalism and racism.
By the late 1800's the United States had expanded all the way across the continent and many of the resources had been claimed or developed. Robber barons of the time put pressure on the government to allow them to expand overseas into colonies, and to help secure those lands and then protect them.
The United States was also quite proud of itself in that time frame, believing that America could look European powers eye to eye on the world stage and more than hold its own. Follow the link on the Open Door Note for a good example. The colonies we took were quite strategic, and served as great forward bases for troops and our navy.
American society at the time also was quite racist. There were laws on the books against immigration by Asians. Social tensions with the immigrant groups that had already arrived was common, and many believed the white race, the English language, and the Christian religion were superior, and that we should bring those things to other parts of the world - whether they wanted it or not.
Imperialism refers to the push by a nation to influence and control other countries in a move to expand into their territories. The imperial power will influence policies being established in foreign countries to ensure such policies are suitable to their interests. The need for imperial powers to establish their authority in foreign countries is in line with the concept of empire building, which extends to the control of factors of production and access to markets.
During the 19th century, there was global competition by different powerful nations to expand territories, and the United States was not left behind in the quest for territorial expansion. The United States annexed Hawaii in 1898 and gained control of all of its possessions. Additionally, the nation challenged Spain in their quest to exert authority over territories including Cuba and Philippines. Although the United States entered the war with Spain based on alleged atrocities committed by Spain, the United States had an agenda of its own, which was mainly economic and territorial expansion as seen by the purchase of Guam, Puerto Rico, and the Philippines.
The lure of economic interests and increasing spheres of influence around the world helped the United States become an imperial power. Many believe that part of the reason why the United States engaged in the practice of imperialism was due to the idea of increasing economic gain. For example, when industrialization generated so much income within the United States, there was a natural inclination to expand these wealth generating initiatives outside its borders in other countries. Business interests in these nations had to be protected, and the use of the military and expanding governmental policy to incorporate these holdings as part of a political initiative helped to increase imperialism. This idea of dollar diplomacy moved the United States into Imperialism and its practices.