the practice or policy of expanding a nation's influence or power by acquiring territories or by gaining control over the economic and political spheres of other territories;
e.g. The country's imperialism allowed it to invade and conquer regions all over the world.
(noun)
a system, government, or authority that is established and held by an emperor or empire;
e.g. The country's imperialism exerted its influence over all aspects of its citizens' lives.