Intrude upon (6)
I believe the answer is:
invade
'intrude upon' is the definition.
(I've seen this in another clue)
This is all the clue.
(Other definitions for invade that I've seen before include "Enter another's territory" , "Encroach upon" , "Penetrate other country with armed forces" , "Enter a country by force with an army" , "make unwelcome advances" .)