Forbidden city in Italy (in Italy!), overthrown, initially being isolated (3,2,1,4)
I believe the answer is:
out on a limb
'isolated' is the definition.
(out on a limb can mean isolated or unsupported)
'forbidden city in italy in italy overthrown initially being' is the wordplay.
'forbidden' becomes 'out' (synonyms).
'city in italy in italy' becomes 'milano' (I am not sure about this - if you are sure you should believe this answer much more).
'overthrown' says the letters should be written in reverse.
'initially' indicates taking the first letters.
The first letter of 'being' is 'b'.
'milano' backwards is 'onalim'.
'out'+'onalim'+'b'='OUT ON A LIMB'
Can you help me to learn more?
(Other definitions for out on a limb that I've seen before include "Without support" , "In a precarious position" , "Wing-walking" , "In a vulnerable position" , "Alone and in danger" .)