Harangues that help back clans (9)
I believe the answer is:
diatribes
'harangues' is the definition.
(I've seen this before)
'help back clans' is the wordplay.
'help' becomes 'aid' (synonyms).
'back' shows that the letters should be reversed in order.
'clans' becomes 'tribes' ('tribe' can be a synonym of 'clan').
'aid' written backwards gives 'dia'.
'dia'+'tribes'='DIATRIBES'
'that' acts as a link.
(Other definitions for diatribes that I've seen before include "Harangues" , "impassioned speeches" .)