Imperialism=a policy of extending a country's power and influence through diplomacy or military force. Basically means that a lower country with less power gets taken over by a much bigger and more powerful country.
Imperialism has been known to happen all through out history, as bigger countries have the lust for power and for them to build an empire or to expand.
Most of these times are when the bigger country has to use military force to take over another.
some examples are: England- which wanted to take over many countries such as Guatemala, Tajikistan and the Marshall Islands, and Luxembourg. Spain- Spain has taken all over the west side of the united states once in history and as the Spanish wanted power they went to other weaker countries in central america and some parts of south america. France- the french has always been trying hard to get big pieces of land as Napoleon goes around and starts to take over other smaller countries which are parts of Canada, and other parts of Africa. And last one is Germany- as the Germans had many failure in doing some imperialism, that soon changed as Adolf Hitler made the country stand up and take control over Netherlands, Belgium, Luxembourg, France, Denmark, Yugoslavia, Greece, Norway and Western Poland.