Capital that is accepted by both sides in promoting Chinese principle (9)

I believe the answer is:

pyongyang

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'capital' is the definition.
(Pyongyang is an example)

'that is accepted by both sides in promoting chinese principle' is the wordplay.
'that' becomes 'yon' (archaic term meaning 'that').
'is accepted by' is an insertion indicator.
'both sides in' means to remove the middle letters (only the side letters remain).
'chinese principle' becomes 'yang' (I have seen 'philosophical principle' mean 'yang' so perhaps 'principle' could also mean 'yang'. I am not sure about the 'chinese' bit.**).
'promoting' with its centre removed is 'pg'.
'yon' going within 'pg' is 'pyong'.
'pyong'+'yang'='PYONGYANG'

Can you help me to learn more?

(Other definitions for pyongyang that I've seen before include "Capital of North Korea" , "North Korean capital" .)

I've seen this clue in The Times.

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