Pledge of united resistance in south-eastern municipality (8)
I believe the answer is:
security
'pledge' is the definition.
(I know that security is a type of guarantee)
'united resistance in south-eastern municipality' is the wordplay.
'united' becomes 'U' (abbreviation).
'resistance' becomes 'r' (electronics abbreviation).
'in' indicates putting letters inside.
'south eastern' becomes 'se'.
'municipality' becomes 'city' (city is a kind of municipality).
'u'+'r'='ur'
'se'+'city'='secity'
'ur' going within 'secity' is 'SECURITY'.
'of' is the link.
(Other definitions for security that I've seen before include "protection or surety" , "cover" , "Freedom from anxiety or fear" , "Protection from possibility of future financial difficulty" , "Safety, protection" .)