Left the nice broken beer mug in principality (13)
I believe the answer is:
liechtenstein
'principality' is the definition.
(I know that Liechtenstein is a principality)
'left the nice broken beer mug' is the wordplay.
'left' becomes 'l' (common abbreviation).
'broken' is an anagram indicator.
'beer mug' becomes 'stein' (synonyms).
'the'+'nice'='thenice'
'thenice' anagrammed gives 'iechten'.
'l'+'iechten'+'stein'='LIECHTENSTEIN'
'in' acts as a link.
(Other definitions for liechtenstein that I've seen before include "Principality between Austria and Switzerland" , "Land" , "Small European country" , "Principality of central Europe" , "Landlocked Alpine principality, capital Vaduz" .)