Country fellows breaking into song (7)
I believe the answer is:
armenia
'country' is the definition.
(Armenia is a country)
'fellows breaking into song' is the wordplay.
'fellows' becomes 'men' (fellow can mean a man).
'breaking into' is an insertion indicator.
'song' becomes 'aria' (piece of music in an opera).
'men' put into 'aria' is 'ARMENIA'.
(Other definitions for armenia that I've seen before include "Former Russian republic, its capital Yerevan" , "Republic in N W Asia" , "Landlocked country south of Georgia" , "Landlocked country, an Asian soviet before 1991, capital Yerevan" , "Republic formerly in the USSR" .)