1. Explanation and example
Imperialism
Explanation and example

2. definition
When an empire or kingdom (in modern society, a country) extends its power by acquiring new territories.
Great Britain is famous for this. Almost every corner of the earth has been a British colony at one time: India, Hong Kong, Myanmar, Australia, the Congo, South Africa, and, most notably, THE UNITED STATES OF AMERICA
Often, the body doing the acquiring exploits the members of the territory being acquired.

3. examples
Cuba
The US has a long relationship with Cuba which originally had to do with the importation of raw materials from Cuba, such as sugar, tobacco, and iron.
Cuba was controlled by Spain until their war for independence in 1895.
Cuba looked to the US for help in their fight for independence from the Spanish.
Cuba achieved formal independence in But in 1901, the U.S. Congress passed the Platt Amendment. This amendment, which was incorporated into the Cuban constitution until 1934, set conditions for U.S. intervention in Cuba’s domestic affairs.
By the 1950s, the U.S. controlled 80 percent of Cuban utilities, 90 percent of Cuban mines, close to 100 percent of the country’s oil refineries, 90 percent of its cattle ranches, and 40 percent of the sugar industry. Cuba also became an investor paradise for U.S. gambling syndicates, real estate operators, hotel owners, and mobsters.

4. examples
China
In the 1800s China was a successful agricultural based economy with leader need or desire to trade with European countries; however, GB wanted to trade with them, as they had lots of stuff the Brits wanted.
The British East India company finally found one good they knew the Chinese couldn’t resist (because no one can, hello, it’s addictive): opium
This was the start of the Opium War
As a result of war, the British were given Hong Kong
Although British imperialism never politically took hold in mainland China, as it did in India or Africa, its cultural and political legacy is still evident today. Honk Kong remains a significant center of global finance and its government still functioned in much of the same ways as it did under British colonialism. Furthermore, the language of English and British culture highly impacted the society of Hong Kong and Southern China for over a century.

5. examples
Vietnam
Our war with Vietnam in the 1960s was an ideological one
Capitalism = good, Communism = bad
Aside from China and the Soviet Union (despite the US’s best efforts) the US was successfully spreading the capitalist ideology all over the world
The thinking was, if we can stop Vietnam from being communist, then other South East Asian countries (Laos, Cambodia, Thailand) would follow.
But the Vietcong won.