US claims special treatment for Chicago and Oklahoma! (8)

I believe the answer is:

musicals

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

'treatment for chicago and oklahoma' is the definition.
I can't tell whether this definition defines the answer.

'us claims special' is the wordplay.
'special' indicates anagramming the letters.
'us'+'claims'='usclaims'
'usclaims' anagrammed gives 'MUSICALS'.

Can you help me to learn more?

(Other definitions for musicals that I've seen before include "Stage shows with songs and dance" , "'South Pacific and Carousel, say (8)'" , "Hair and Grease" .)

I've seen this clue in The Guardian.

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