Alliance formed when bar not closed (4)
I believe the answer is:
bloc
'alliance' is the definition.
(bloc is a kind of alliance)
'bar not closed' is the wordplay.
'bar' becomes 'block' (synonyms).
'not closed' means to remove the last letter.
'block' with its last letter taken off is 'BLOC'.
'formed when' acts as a link.
This may not be right. Some or all of it may be part of another bit of the clue.
Can you help me to learn more?
(Other definitions for bloc that I've seen before include "Political allies" , "International alliance" , "Political group of nations" , "Political grouping of countries" , "Allied country group" .)