abroad. Therefore, it seemed natural that American power should extend outside North America—especially toward the Pacific Ocean.

Howard Zinn, the prominent American historian, argued that America's economic elite was a driving force behind imperialism. American businesses sought foreign markets. America's workers, on the other hand, did not gain from colonial ventures.

The Spanish-American War (1898) made America a colonial power. Cuban rebels had been fighting for independence from Spain, and the U.S. declared war against Spain after the USS Maine was destroyed by a mysterious explosion. After Spain was defeated, the U.S. gained control over Cuba, the Philippines, and a number of smaller islands.

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.

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.

The United States became an imperial power during the late nineteenth century in order to spread American idealism and commercialism. Thanks to the works of Alfred Thayer Mahan, which stated that a nation needed a strong navy in order to create an empire, the United States looked to the Pacific in order to obtain coaling stations for its ships.

Pineapple plantation owners overthrew the queen of Hawaii in order to establish an American territory. The president at the time, Grover Cleveland, turned down their request but his successor, William McKinley, signed off on the land grab.

The United States also annexed Guam and the Philippines as the result of the Spanish-American War. This war started under the guise of removing harsh Spanish rule from Cuba and Puerto Rico, when in reality it was more for protecting American interests on the islands. Though many Filipinos helped fight for their own freedom, their request for nationhood was turned down, thus leading to the Filipino War which killed more Americans than did the conflict with Spain.

The United States also assisted Panama in gaining its independence from Colombia. This was not done out of a sense of giving the Panamanians a country; rather, it was to dig the Panama Canal. The Canal Zone would remain a US territory throughout the twentieth century.

In the twentieth century, the United States increased its actions abroad by brokering the Open Door Policy with China which did away with the spheres of influence held by various European nations and Japan. The United States wanted China to remain open for trade. The United States also sent troops to Mexico during its revolutions prior to WWI in order to ensure governments friendly to its oil interests in the country. Prior to WWI, the United States sent a force under John Pershing to capture Pancho Villa, though they were unsuccessful.

"Imperial power" is a bit of a vague label. It tends to mean several things at once, so let's unpack it.

In the sense of "this country was built on conquest by force," the "imperial power" part of America actually predates the United States proper. The territories that would become the United States were imperial colonies, established by the great European empires of the 17th and 18th centuries. Much of the US Constitution and American governance generally goes back to England, history's largest and most successful imperial power, but vital aspects of American culture come from other imperial powers, such as France and Spain. Much of American culture comes from sources other than the old empires, but they were key influences on what the United States became.

In the sense of "this country treats conquest by force as a fundamental component of its culture, economy and politics," the United States has always been an imperial power. Even early in American history, the War of 1812 included an invasion and attempted occupation of British Canada (see reference), and the Mexican War was fought to claim new colonies from Spanish Mexico. Above all, from the moment of our founding until well into the modern age, United States history has been defined by an ongoing conquest by force of territories occupied by American Indians. The key concept is "manifest destiny," the belief that European-descended Christians had a God-given right, indeed a God-given duty, to conquer the North American continent, and that the cultures that already existed there were without value. Similar ideas were used as justification for other imperial powers, most famously in Britain with what Kipling called "the white man's burden."

If you're interested in when the system that exists now, within the borders that exist now, started conquering things outside those borders by force, the United States became an imperial power in the 1890s. That unsurprisingly coincides with the end of organized military conflict between the US Army and American Indians. In short, the United States started conquering things outside its borders—that is, the borders the US thought it was entitled to, according to manifest destiny—as soon as it was done conquering things inside them. Most historians link the beginning of this phase of American imperialism to the Spanish-American War. The Spanish-American War made the United States an "overseas empire" for the first time, one that included the territories of Guam, Hawaii (then the Sandwich Islands), the Philippines and Puerto Rico (see reference). Guam, Hawaii, and Puerto Rico remain American possessions today.

That said, it's important to remember that while the Spanish-American War resulted in the first overseas territories claimed by the United States, America as it exists now was built on conquest by military force. The United States has been an imperial power since its founding.

The United States became an imperial power at the end of the 1890s. The United States wanted to gain colonies around the world. We knew we probably were going to have to go to war to do this. When we learned about how poorly the Spanish were treating the people of Cuba, we wanted to help the people of Cuba. After a series of incidents, we went to war against Spain in 1898. As a result of the Spanish-American War, we got Puerto Rico, Guam, and the Philippines from Spain. We were now a world power.

As we became a world power, we needed to build up our navy. We knew that world powers must be able to protect their trade. We also knew that world powers needed bases around the world where their ships could stop, resupply, and refuel. Thus, the Great White Fleet was built to develop and show off our naval power. This fleet was used to help Panama become independent. It also sailed around the world to show the military might of the United States.

By defeating Spain in the Spanish-American War and by building up our navy, the United States became a world power in the 1890s.