Peninsula forming a large part of America (6)

I believe the answer is:

crimea

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'peninsula' is the definition.
(I know that Crimea is a peninsula)

'a large part of america' is the wordplay.
'a large part of' becomes 'crime' (I am not sure about this - if you are sure you should give a lot more credence to this answer).
'america' becomes 'a' (common abbreviation - e.g. in organisation names).
'crime'+'a'='CRIMEA'

'forming' is the link.

Can you help me to learn more?

(Other definitions for crimea that I've seen before include "former battleground" , "part of the Ukraine" , "Yalta peninsula" , "European peninsula" , "Peninsula in today's Ukraine, site of an 1853-6 war" .)

I've seen this clue in the Evening Standard.

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