D'Artagnan at once embraces group that's all for one (4)
I believe the answer is:
nato
'group that's all for one' is the definition.
I can't judge whether this defines the answer.
'd'artagnan at once embraces' is the wordplay.
'embraces' indicates the answer is hidden within the clue (I've seen 'embraced' mean this).
'NATO' is hidden within 'dartagnan at once'.
Can you help me to learn more?
(Other definitions for nato that I've seen before include "Military alliance (acronym)" , "International organisation for collective security" , "N. Atlantic alliance" , "Military/political alliance" , "Collective security alliance engaged in Bosnia" .)