Mother country's doom (9)
I believe the answer is:
damnation
'doom' is the definition.
(thesaurus)
'mother country's' is the wordplay.
'mother' becomes 'dam' (female parent of an animal).
'country' becomes 'nation' ('nation' can be a synonym of 'country').
'dam'+'nation'='DAMNATION'
(Other definitions for damnation that I've seen before include "27 [HELL]" , "Curse" , "Infernal punishment" , "Eternal punishment" , "Denouncing" .)