Answer :

a policy of extending a country's power and influence through diplomacy or military force."the struggle against imperialism
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historical rule by an emperor." 
 the effect that a powerful country or group of countries has in changing or influencing the way people live in other, poorer countries

Imperialism can refer to a state policy, an ideology, a practice or an advocacy of extending power and dominion, usually by means of territorial acquisition -using military forces- or political or economic control over other areas. The aim is to extend a nation's rule over foreign nations. Since it always involves the use of power over another party, imperialism has often been considered morally reprehensible.