Modern nation frequently requiring compassion (5-2-3-3)
I believe the answer is:
state-of-the-art
'modern' is the definition.
(I've seen this before)
'nation frequently requiring compassion' is the wordplay.
'nation' becomes 'state' (synonyms).
'frequently' becomes 'oft' (oft can mean frequently, eg oft-quoted).
'requiring' is a charade indicator (letters next to each other).
'compassion' becomes 'heart' (I've seen this before).
'state'+'oft'+'heart'='STATE-OF-THE-ART'
(Other definitions for state-of-the-art that I've seen before include "Incorporating the newest ideas and features" , "Modern" , "Produced by the latest technology" , "Most up-to-date of its type" , "Up-to-the-minute" .)