Takeover, due to pact collapsing (4,5)
I believe the answer is:
coup detat
'takeover' is the definition.
(I have seen 'Hostile takeover' mean 'coup detat' so perhaps 'takeover' could also mean 'coup detat')
'due to pact collapsing' is the wordplay.
'collapsing' is an anagram indicator.
'due'+'to'+'pact'='duetopact'
'duetopact' anagrammed gives 'COUP DETAT'.
(Other definitions for coup detat that I've seen before include "Sudden illegal seizure of government" , "Violent seizure of power from a government" , "Seizure of the levers of power" , "Sudden, perhaps violent, overthrow of a government" , "Acted up to, involved in sudden overthrow of government" .)