Change of government has to depose king, in theory (9)
I believe the answer is:
evolution
'theory' is the definition.
(I have seen 'Darwinian theory ' mean 'evolution' so perhaps 'theory' could also mean 'evolution')
I cannot understand how the rest of the clue works.
Can you help me to learn more?
(Other definitions for evolution that I've seen before include "it's a gradual process" , "Darwinian theory" , "Darwin's theory" , "Gradual development" , "Gradual change" .)