Goddess brought about emphatic agreement in Mexico (4)
I believe the answer is:
isis
'goddess' is the definition.
(I've seen this before)
'brought about emphatic agreement in mexico' is the wordplay.
'brought about' says the letters should be written backwards.
'emphatic agreement in mexico' becomes 'si si' ('yes! yes!' in Spanish).
'sisi' back-to-front is 'ISIS'.
(Other definitions for isis that I've seen before include "Egyptian goddess and jihadist group" , "Oxford's second eight" , "Sister of Osiris" , "To be, to be an Egyptian goodess" , "where one might take a punt" .)