Barrel-maker had succeeded in works without confrontation (10)

'works without confrontation' is the definition.
(to cooperate is to work productively with others)

'barrel-maker had succeeded' is the wordplay.
'barrel maker' becomes 'cooper' (synonyms).
'had' becomes 'ate' (e.g. I had an ice cream).
'succeeded' becomes 's' (genealogical abbreviation).
'cooper'+'ate'+'s'='COOPERATES'

'in' acts as a link.