Upset South American alliance about capital of Colombia - or elsewhere? (8)

I haven't cracked this one yet — but the brilliant team at Fifteensquared have:

S (abbreviation for south) + A (abbreviation for American), reversed (upset = upwards in a down clue), then UNION (alliance) around the first letter (capital) of C [olombia]. Extended definition: Asunción isn’t the capital of Colombia, but it is the capital of Paraguay.