Justify tirade following conflict (7)
I believe the answer is:
warrant
'justify' is the definition.
('warrant' can be a synonym of 'justify')
'tirade following conflict' is the wordplay.
'tirade' becomes 'rant' (I've seen this before).
'following' means one lot of letters go next to another.
'conflict' becomes 'war' (war is a kind of conflict).
'rant' after 'war' is 'WARRANT'.
(Other definitions for warrant that I've seen before include "Justify; authorisation" , "Document giving authority" , "Call for" , "Merit, justify" , "Permit for arrest, search of premises, etc" .)