Justify sabre-rattling diatribe? (7)

I believe the answer is:

warrant

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'justify' is the definition.
(I know that warrant is a more specific form of justify)

'sabre-rattling diatribe?' is the wordplay.
'sabre rattling' becomes 'war' (I can't explain this - if you can you should believe this answer much more).
'diatribe?' becomes 'rant' (I've seen this in other clues).
'war'+'rant'='WARRANT'

Can you help me to learn more?

(Other definitions for warrant that I've seen before include "Call for" , "Permit for arrest, search of premises, etc" , "Authorise, justify" , "Travel pass" , "Writ for arrest" .)

I've seen this clue in The Sun.

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