Sergeant may revert to former state (4,7)

I believe the answer is:

east germany

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

'former state' is the definition.
(I've seen this before)

'sergeant may revert' is the wordplay.
'sergeant may' can be anagrammed to 'EAST GERMANY'.
Though, I'm not clear how this is indicated.

'to' is the link.

Can you help me to learn more?

(Other definitions for east germany that I've seen before include "Former state" , "GDR, before 1990" .)

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