A call in troubled East for a coalition (8)
I believe the answer is:
alliance
'a coalition' is the definition.
(alliance is a kind of coalition)
'a call in troubled east' is the wordplay.
'troubled' indicates anagramming the letters.
'east' becomes 'e' ('E' can be a synonym of 'east'**).
'a'+'call'+'in'='acallin'
'acallin' anagrammed gives 'allianc'.
'allianc'+'e'='ALLIANCE'
'for' is the link.
(Other definitions for alliance that I've seen before include "Group acting together for common cause" , "Marriage - union" , "Combination by treaty" , "The joining by political agreement or treaty" , "Coalition or union" .)