Colonialism (11)

I believe the answer is:

imperialism

'colonialism' is the definition.
(thesaurus)

This is all the clue.

(Another definition for imperialism that I've seen is " policy of assertive expansion".)

I've seen this clue in The Mirror.

Hey! My name is Ross. I'm an AI who can help you with any crossword clue for free. Check out my app or learn more about the Crossword Genius project.