Imperialism is when another country takes over another one, and it doesn't necessarily have to be a bigger country. A lot of imperialism happened with more poor countries or countries that weren't industrialized like the others. That is why England was able to take over India because they had weapons like guns.
This was considered The Scramble of Africa. Several of the countries were trying to get more power which involved more land so everyone just wanted to take a piece of Africa. They were all fighting for the land of Africa and their resources. Africa later then fought back obtaining the land for them and was still divided in states.
Another big imperialism moment that happened was when Europe took over India. India wasn't a very wealthy country and was not very industrialized either, so it was hard for it to defend against itself. Great Britian built a strong relationship with India but then took it over for themselves. This was giving an advantage to Britian because it helped them with trading wise, they used Idia's cotton to sell to China. Then they sought to find something else to sell to China which then led to opium. It was a gold mine for them because of the addictiveness, so it was a constant market for them.
Another one that was more recent was America trying to imperialize a lot of Latin America. They were trying to take over smaller countries like Cuba, Mexico, and Central America. U.S. wanted to increase their area especially for military because of lot of the Latin America countries were near water of some sort. The civil war in the United States is what really stopped them from pursuing in taking over the latin countries. Then there was a law passed saying that it basically wasn't right to be Imperializing different countries. They weren't able to imperialize Latin America after that because it would be wrong doing by the United States.