Closing of border facilitates attacks (5)
I believe the answer is:
raids
'attacks' is the definition.
(I know this)
'closing of border facilitates' is the wordplay.
'closing of' says to take the final letters.
'facilitates' becomes 'aids' (I've seen this in another clue).
The last letter of 'border' is 'r'.
'r'+'aids'='RAIDS'
(Other definitions for raids that I've seen before include "Sudden attacks" , "Searches by police without warning" , "Surprise attacks" , "Invasions" , "Military attacks" .)