Revised pact due to unexpected change of government (4,5)
I believe the answer is:
coup detat
'unexpected change of government' is the definition.
I can't tell whether this defines the answer.
'revised pact due to' is the wordplay.
'revised' indicates anagramming the letters.
'pact'+'due'+'to'='pactdueto'
'pactdueto' with letters rearranged gives 'COUP DETAT'.
Can you help me to learn more?
(Other definitions for coup detat that I've seen before include "Acted up to create sudden overthrow of government" , "leadership change" , "Sudden, perhaps violent, overthrow of a government" , "Acted up to, involved in sudden overthrow of government" , "Sudden illegal seizure of government" .)