It was a fully unified country way before 1929, unless you are counting Alto Adige and Trieste as conditio sine qua non to have a fully unified Italy, which I wouldn’t.
It was a confederacy of loosely associated city states which were sometimes at war with one another going on for centuries.
I know this opens up "The United States can't claim a full 250 years on account of that frackus in the 1860s" and I'm fine with that. But I will strongly contend that when your city raises an army to try and sack your nation's capital, you are no longer living in a historically contiguous country.
Naples up and did its own thing several times from the 18th-20th century. Nevermind how many people had to die fighting the Italian Wars of Independence.