Beginning with the Louisiana Purchase of 1803, the United States had seen a steady westward expansion throughout the 19th century. This expansion was driven in part by the ideal of Manifest Destiny, the widely-held belief that America was destined to expand across the continent to the Pacific Ocean, driving all opposition before them.

Unprecedented Growth

In the decades following the Civil War, American industrialism grew enormously. Mass production techniques and the expansion of factories meant that stores were filled with an unprecedented number of consumer goods. Waves of immigrants provided workers for farms and factories -- and these immigrants became consumers, as well. With railroads now connecting the entire country, goods were available to an ever-widening market. Crop yields increased as farmers, too, took advantage of mechanization to grow crops more efficiently.

Expansion Overseas

Factories and farms produced more than the public could buy, leading to surpluses that resulted in financial panics in 1873 and 1893. It was obvious to the American government that new markets were needed for American goods. Thus American foreign policy makers began to look to foreign countries to provide these markets and were influenced by the work of British writer Captain Alfred Thayer Mahan. Mahan's book “The Influence of Sea Power Upon History” postulated that Britain’s rise to world power began with control of the seas. The United States government was also impressed by the work of Professor Frederick Jackson Turner, whose 1893 essay “The Significance of the American Frontier” argued forcibly that, with westward expansion now over, the United States government must build a merchant navy and a strong fleet to protect overseas interests.

Cementing U.S. Interests

In 1898, America defeated Spain in the Spanish-American War, forcing her to give up Cuba, Puerto Rico, the Philippines and Guam. The war gave the U.S. the excuse it needed to annex Hawaii in 1898, since it would provide an important strategic naval base to protect growing U.S. interests in the Pacific and Asia. After the assassination of President William McKinley in 1901, Theodore Roosevelt took office. He continued the American foreign policy that had begun in the 1890s, warning European governments that the United States would defend the Western Hemisphere against foreign interference. He began the construction of the Panama Canal, which was highly beneficial to U.S. merchant interests.

Imperialism?

In the end, both American citizens and those shaping American foreign policy were still influenced by Manifest Destiny -- “the unconquerable energy” of the Anglo-Saxons in America, as Republican Senator Henry Cabot Lodge called it in 1896. Others knew it by another name -- Imperialism -- but by the end of the 19th century it was a fait accompli.