Imperialism: When a stronger country gains control of a younger country through Diplomacy or Military force.
Examples of Imperialism:
Hundreds of years ago, Great Britain was the greatest Empire in the world, it took control of North America, Scotland, Australia, India and many countries in Africa
When Europe started colonizing the Americas, Spain took control of a huge majority of Central and South America. Today these countries are Mexico, Peru, Argentina, and Chile
The Soviet Union
After WW2, The Soviet Union began taking over countries and spread communism. It started a nuclear arms race with the U.S. and even took over some countries in Asia and Eastern Europe. These conflicts started off the Cold, Korean, and Vietnam wars
In ancient times, Rome ruled the world. With a strong republic and a powerful military, Rome was expanding constantly, bringing new countries and places under it's rule, which turned it into an empire and eventually fell.