Why does a nation seek to do if it has a policy of imperialism

The definition of Imperialism is building empires by expanding territory and gaining colonies. Nations would want to colonize other areas because there was competition between Industrializations. People also believed that the "strong" (nation) should take over the weak (nation). The White Man's Burdan was also a cause of Imperialism because it claims that people duty was to 'civilize' people of other nations. (I did not google this. This is what I learned in school.)