Facts:

800 years ago, Ireland became the first colony of what later became known as the British empire. 

Imperialist military interventions become matters of "national defense," "national security," and maintaining "stability" in one or another region

Imperialism is older than capitalism.Capitalist imperialism differs from these earlier forms in the way it systematically accumulates capital through the organized exploitation of labor and the penetration of overseas markets

Imperialism forces millions of children around the world to live nightmarish lives, their mental and physical health severely damaged by endless exploitation like in countries like Mexico, India, Colombia, and Egypt, children are dragooned into health-shattering, dawn-to-dusk labor on farms and in factories and mines for pennies an hour, with no opportunity for play, schooling, or medical care.

After World War II, European powers like Britain and France adopted a strategy of neoimperialism. Left financially depleted by years of warfare, they discovered that the removal of a conspicuously intrusive colonial rule made it more difficult for nationalist elements within the previously colonized countries to mobilize anti-imperialist sentiments.

Imperialism is the domination of the economic, political, and cultural life over another nations or countries. It begun in the 1800’s, which European countries controlled Africa, Asia, and South America.

The Western Empire succeed because they established empires. Many Europeans believed in Social Darwinism during the imperialism period, in the 1800’s. Social Darwinism is the survival of the fittest. 

United States took over the Californian and some parts of western territories after the Gadsden purchase and Treaty of Guadalupe Hidalgo. This imperialism expanded the area of United States. 

The political and military control of United States can be seen after the World War II.  In May, the military occupied Austria and Germany. In September 1945, the military of US occupied the areas of Korea and Japan.

One of the supporters of American imperialism is Alfred T. Mahan. In the 19th century, This man was the officer in US Navy.  If you check his book The Influence of Sea Power upon History published in 1890, he supported the imperialism of America to other countries.\

Resources: 

http://www.historyisaweapon.com/defcon1/imperialism.html

http://funfactsinformation.weebly.com/the-new-imperialism.html

http://factfile.org/10-facts-about-american-imperialism