Country not upset over general assembly at first (5)
I believe the answer is:
tonga
'country' is the definition.
(I know that Tonga is a country)
'not upset over general assembly at first' is the wordplay.
'upset over' says the letters should be written in reverse (knocked over).
'at first' indicates taking the first letters.
The first letters of 'general assembly' is 'ga'.
'not' in reverse letter order is 'ton'.
'ton'+'ga'='TONGA'
(Other definitions for tonga that I've seen before include "Polynesian Kingdom" , "Pacific Ocean kingdom" , "SW Pacific monarchy" , "The Friendly Islands" , "Pacific island state" .)