Imperialism can be defined as a strong country conquering a weaker country by military strategy or by diplomacy.
Now I have to write four examples of this. If I could choose to not do this, I would not do this, but it is not my choice to make, so I guess I have to write four examples of imperialism.
Darth Vader is imperialistic. You can know this because the empire takes over a bunch of small planets and systems that are weaker than the empire. You can also know this because of the song, the imperial march. But he isn't one of the examples, because he's not from around this world, but rather from a world a long time ago, in a galaxy far, far away.
Napoleon Bonaparte was imperialistic as well. While he was alive and emperor of France, he became very ambitious and conquered many countries. These countries were weaker, and therefor he exercised imperialism.
The United States of America use imperialism over Puerto Rico, several years ago on Texas, Guam, and other states, islands, and other stuff. The USA has exercised dominion, if you will, over these areas, and Texas was actually won through a war with Mexico, and USA took over this area because of greater strength, therefore classifying it as imperialism. We are also in charge of Puerto Rico and Guam, both of which are considered commonwealths of the USA.
Example number three is how Spanish Conquistadors went out on boats and found places to conquer. They found many countries and islands that they took over because they were stronger than these places. You can still find a remnant of the Spanish culture in Mexico, where Spanish is the most spoken language.
The last example is the easiest; Great Britain conquered lots of places. They have dominion over Canada, many African countries, Scotland, other European countries, and of course, until we decided to be independent, over the USA. Brits were really good at doing this and they still are in charge of tons and tons and tons of islands, countries, etc.