Measure to avoid disorder in South American diplomacy? (4,3)
I believe the answer is:
riot act
'measure to avoid disorder' is the definition.
(legislation meant to stop riots)
'south american diplomacy?' is the wordplay.
'south american' becomes 'rio' (I can't explain this - if you can you should give a lot more credence to this answer).
'diplomacy?' becomes 'tact' (tact can mean diplomacy or sensitivity).
'rio'+'tact'='RIOT ACT'
'in' acts as a link.
Can you help me to learn more?
(Other definitions for riot act that I've seen before include "Citator may read this as stern rebuke" , "Statute against rowdy behaviour" , "measure to keep order" , "used to control disorder" , "Old law designed to disperse a mob" .)