A simple Riley riddle. Watch the tags!
My prefix feels not so lucky in Rome.
My infix denotes the Third Rome.
My suffix plays in the brass band.
My whole created a new country.
The answer is:
1776 - the year the US declared independence from the British Empire. ('My whole created a new country.')
My prefix feels not so lucky in Rome.
The number 17 is considered unlucky in Italy - a notion that dates back to Ancient Roman times.
My infix denotes the Third Rome.
'The Third Rome' is often considered to be the Russian capital, Moscow. One of the region numbers for Moscow that appears on Russian license plates is 77.
My suffix plays in the brass band.
This is a reference to the song 'SEVENTY-SIX Trombones', a song whose lyrics revolve around a brass band.
Put these all together (with overlap), and we have:
the year 1776! The mathematics tag here leads us to the use of numbers rather than words in this puzzle, and the international flavour of the lines (via references to Italy and Moscow) ties in nicely with the significance of the year in the history of another country - the United States of America...