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A threads post saying "There has never been another nation ever that has existed much beyond 250 years. Not a single one. America's 250th year is 2025. The next 4 years are gonna be pretty interesting considering everything that's already been said." It has a reply saying "My local pub is older than your country".
I'll spot you at least a few of these. But the Vatican was incorporated in 1929 precisely because they needed to delineate between the Italian city of Rome and the Bishopry of the Catholic Church. Italy wasn't a fully unified country until about a decade earlier.
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.
As for the Vatican situation, the Italian kingdom completely conquered and annexed the papal state in 1870 (Breccia di Porta Pia).
In 1929 the Pope formed an alliance with Mussolini to get a state in exchange for the approval of the fascist government from the Church (and other stuff, but that's the gist of it)
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.