Socialists abandoned arms without hesitation (4-7)
I believe the answer is:
left-wingers
'socialists' is the definition.
('left-winger' can be a synonym of 'socialist')
'abandoned arms without hesitation' is the wordplay.
'abandoned' becomes 'left' (I've seen this before).
'arms' becomes 'wings' (I can't justify this - if you can you should believe this answer much more).
'without' means one lot of letters goes inside another ('without' can be similar in meaning to 'outside').
'hesitation' becomes 'er' (sound used when hesitating).
'wings' enclosing 'er' is 'wingers'.
'left'+'wingers'='LEFT-WINGERS'
Can you help me to learn more?
(Another definition for left-wingers that I've seen is " Socialists".)