A leader upset about western state (8)
I believe the answer is:
delaware
'state' is the definition.
(I know that Delaware is a American state)
'a leader upset about western' is the wordplay.
'upset' indicates anagramming the letters.
'about' is an insertion indicator.
'western' becomes 'w'.
'a'+'leader'='aleader'
'aleader' anagrammed gives 'delaare'.
'delaare' placed around 'w' is 'DELAWARE'.
(Other definitions for delaware that I've seen before include "State of eastern US" , "One of the original 13 US states" , "American state, capital Dover" , "US state and river" , "Second smallest US state" .)