China was broken by this, used as a weapon (8)

I believe the answer is:

chainsaw

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Here is my best explanation:

'this used as a weapon' is the definition.
The definition suggests a singular noun which matches the answer.

'china was broken' is the wordplay.
'broken' is an anagram indicator.
'china'+'was'='chinawas'
'chinawas' anagrammed gives 'CHAINSAW'.

'by' acts as a link.

Can you help me to learn more?

This clue was last seen in Evening Standard