Working men in Black Country (7)
I believe the answer is:
Here is my best explanation:
'country' is the definition.
(Denmark is an example)
'working men in black' is the wordplay.
'working' indicates anagramming the letters.
'in' indicates putting letters inside.
'black' becomes 'dark' ('dark' can be a synonym of 'black'**).
'men' with letters rearranged gives 'enm'.
'enm' put into 'dark' is 'DENMARK'.
(Other definitions for denmark that I've seen before include "EU member", "Mark end of the country", "kingdom", "Hamlet's country", "North European country", "European monarchy", "Hamlet's homeland", "Copenhagen its capital", "A country of dark men?" and "Ditto".)