Could possibly mollify aggressive Yemeni leaders (3)
I believe the answer is:
may
'could' is the definition.
(I've seen this before)
'mollify aggressive yemeni leaders' is the wordplay.
'leaders' suggests taking the first letters.
The initial letters of 'mollify aggressive yemeni' is 'MAY'.
'possibly' is the link.
(Other definitions for may that I've seen before include "Hawthorm blossom" , "'5 _____' (popular piece of music by Bach)" , "The permissive month" , "maid" , "Fifth month" .)