Island nearly destroyed, invaded by desperate extremists (8)
I believe the answer is:
alderney
'island' is the definition.
(I've seen this before)
'nearly destroyed invaded by desperate extremists' is the wordplay.
'destroyed' indicates anagramming the letters.
'invaded by' indicates putting letters inside.
'desperate' becomes 'dire' (I've seen this before).
'extremists' says to hollow out the word (remove centre letters).
'dire' with its centre removed is 'de'.
'nearly' anagrammed gives 'alrney'.
'alrney' placed around 'de' is 'ALDERNEY'.
(Other definitions for alderney that I've seen before include "One of Channel Islands" , "Cow, perhaps" , "Channel isle" , "A Channel Island" , "Third largest of the Channel Islands" .)