Enter by force to conquer (6)
I believe the answer is:
invade
'enter by force to conquer' is the definition.
(I've seen this before)
This is the entire clue.
(Other definitions for invade that I've seen before include "Violate" , "Penetrate harmfully, country or body" , "Enter illegally" , "infect" , "Enter a country by force with an army" .)