Centrists baffled by southern authoritarianism (10)

I believe the answer is:

strictness

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'authoritarianism' is the definition.
Although both the answer and definition are singular nouns, I don't see how they can define each other.

'centrists baffled by southern' is the wordplay.
'baffled' indicates an anagram.
'by' is a charade indicator (letters next to each other).
'southern' becomes 's' (abbreviation).
'centrists' anagrammed gives 'strictnes'.
'strictnes'+'s'='STRICTNESS'

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I've seen this clue in the Sydney Morning Herald.

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