• in the Pacific, to expand its strategic reach. This was also a major motive in gaining Hawaii as well as other Pacific islands like Guam.
• Ideological motives: These ranged from a sincere desire to spread Christianity on the part of Protestant ministers to a belief in the racial and cultural superiority of Americans. Either way, many imperialists believed that they had a natural or God-given right to exercise dominion over peoples around the world. 

The forces pushing American expansion overseas included the idea that America had already exhausted its frontier but needed the frontier to allow people in the democracy to continually reinvent themselves. This idea, referred to as the "Turner Thesis," came from Frederick Jackson Turner, a historian who presented the idea in the 1890s that the American frontier had closed but that the frontier had made the country distinctly American. As a result, people felt that they needed to expand overseas in search of a new frontier.

Another force compelling American imperialism was the ideas of Alfred Thayer Mahan, a naval historian who wrote The Influence of Sea Power Upon History in 1890. His thesis was that great empires possess sea power, and this idea also compelled the American government to establish naval bases abroad.

In addition, the economic depression that started in 1893 convinced experts such as Mahan that the U.S. needed markets overseas to absorb the excess domestic goods that were being produced. These impulses, along with the desire for the raw materials that overseas empires could produce, propelled American imperialism. 

The U.S. began expanding oversees for many different reasons. One of the earliest factors was lucrative overseas trade opportunities. By the mid 1800’s, American merchants carried on a profitable trade with Asia and hoped to expand the market into other areas. Japan was opened to American trade in 1854, and the new trade opportunities got the U.S. more interested in further expansion, which led to greater U.S. involvement in Asia.

The search for markets and materials drove the U.S. to more expansion. Some politicians, like Secretary of State Seward, dreamed of an American empire similar to those in Europe. This would allow the U.s. to take what they saw as their rightful place at the center of power. Seward purchased Alaska in 1867, which soon revealed a fortune in gold and natural resources.

Some Americans believed that a good reason for expansion into other countries was to “lift up” those races that were “uncivilized” by sharing Christianity and western civilization. This also promoted movement into Africa, Asia and the Caribbean.

Also, naval power was essential to a nation projecting its power overseas. The U.S. needed overseas colonies where ships could dock to maintain this navy, which eventually allowed the U.S. to become more involved in foreign affairs.

Historians typically cite three main forces that pushed for overseas expansion.  They were:

• Military and political forces.  The US wanted to become a major world power.  Military people, inspired by Alfred Thayer Mahan, felt that a strong navy was the key to this.  This meant that a wide network of naval bases would be needed.
• Economic forces.  American industrialists wanted new sources of raw materials and new markets in which to sell.
• Cultural forces.  People like Theodore Roosevelt wanted to prove America’s toughness and superiority through expansion.  Others felt that the US had a mission to civilize and improve the rest of the world.

There are three main reasons why the United States engaged in colonization in the late 1800s and early 1900s.  One reason was economic while the other two had to do with power in the international arena.

One reason why Americans wanted to take colonies was to make the country richer.  Americans believed that taking colonies would give them access to more resources.  For example, by taking Hawaii, the US got access to the sugar that the islands produced.  In addition, colonization would give them more markets in which to sell.  Countries that the colonized would be more likely to buy manufactured goods and other products from the US.  In these ways, colonization would boost the US economy.

In the international arena, colonization was seen as a way to increase American military power.  The American naval thinker Alfred Thayer Mahan said that countries could only be strong if they had naval power.  By taking colonies, the US would get itself more places to put naval bases like the one at Pearl Harbor.  This would enhance its ability to project military power around the world.

Also in the international arena, having more colonies would make the United States more of a world power.  All of the major European countries had colonies in various places around the world.  If the US wanted to be seen as a world power on a par with those countries, it had to have colonies of its own.

Thus, there were at least three main reasons why the US engaged in colonization in the late 1800s and early 1900s.