Dilemma if America holds mob back (5)

I believe the answer is:

mafia

I'm a little stuck... Click here to teach me more about this clue!

'mob back' is the definition.
'mafia' can be an answer for 'mob' (I've seen this before). I am unsure of the 'back' bit.

I don't understand the rest of the clue.

Can you help me to learn more?

(Other definitions for mafia that I've seen before include "Criminal organisation with origin in Sicily" , "The Sicily mob" , "Our family" , "International crime organisation originating in Sicily" , "Criminal society" .)

I've seen this clue in The Irish Times.

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