Deal with Yankee, making pact (6)
I believe the answer is:
treaty
'pact' is the definition.
('treaty' can be a synonym of 'pact')
'deal with yankee' is the wordplay.
'deal with' becomes 'treat' ('treat' can be a synonym of 'deal with').
'yankee' becomes 'y' (phonetic alphabet: alpha, bravo, charlie etc.).
'treat'+'y'='TREATY'
'making' is the link.
(Other definitions for treaty that I've seen before include "settlement" , "Contract between states" , "Negotiation" , "Ratified agreement between states" , "International agreement" .)