Huge region in quasi-alliance (4)
I believe the answer is:
asia
'huge region' is the definition.
(I've seen this before)
'in quasi-alliance' is the wordplay.
'in' indicates a hidden word.
'ASIA' is hidden in the letters of 'quasi alliance'.
(Other definitions for asia that I've seen before include "Continent in which India is situated" , "Stretch of land" , "The nations of the East, collectively" , "Earth's largest continent" , "Large continent" .)