Attacked, retreat in turn across country (5)
I believe the answer is:
nuked
'attacked' is the definition.
(to nuke is to attack with a nuclear bomb)
'retreat in turn across country' is the wordplay.
'retreat' becomes 'den'.
'in turn' says the letters should be written in reverse (letters turning around).
'across' indicates putting letters inside.
'country' becomes 'uk' (UK is an example).
'den' back-to-front is 'ned'.
'ned' going around 'uk' is 'NUKED'.
(Other definitions for nuked that I've seen before include "zapped into oblivion?" , "Used bombs" .)