Relations between Argentina and its much smaller neighbour, Uruguay, have been strained in a dispute over a pulp paper mill built on the river that separates the two countries - but, as Daniel Schweimler discovered, a much more serious dispute strikes at the very heart and soul of both nations' identity.
For many Argentines Carlos Gardel embodies the soul of tango
One of the great Argentine icons, alongside footballer Diego Maradona and the former first lady, Eva Peron, is the tango singer, Carlos Gardel.
Pictures of him with his slicked-backed hair and perfectly tailored suits adorn many Argentine bars and restaurants and you will often hear his songs played by Buenos Aires taxi drivers on the all-tango radio stations.
He was an early playboy, an international superstar who came to a tragic and premature end in a plane crash in Colombia in 1935. Gardel is to Argentina what Frank Sinatra is to the United States or Edith Piaf is to France.
A copy of Gardel's birth certificate states he was born in Tacuarembo
So while driving through northern Uruguay recently, I had to take a second look when I saw a sign pointing to Carlos Gardel's birthplace and museum.
How cheeky can you get? It is like Canadians saying that Sinatra was not really born in Hoboken, New Jersey, but in Moose Jaw, Saskatchewan.
Or the British claiming that Edith Piaf really hailed from Basingstoke in southern England.
Gardel is as Argentine as a big lump of juicy steak being barbequed by gauchos out on the pampas. But not according to the Uruguayans, and they have the evidence to prove it - or so they say.
Tango is not just a style of music and dance - it is the beat to which both nations evolved from their immigrant roots
The museum, playing strains of some of his famously dramatic songs, displays a copy of his birth certificate stating very clearly that he was born in Tacuarembo in northern Uruguay.
It tells, in graphic detail, the story of how Carlos Gardel - the Uruguayan tango star, came to be. His father was a local landowner, Carlos Escayola.
When his first wife died, he married her younger sister. But while married to her, had an affair and fathered a child with the third sister, Maria Lelia Oliva, aged just 13.
To avoid scandal the son, young Carlos, was given to a visiting French cabaret dancer - Berta Gardes who Escayola, just for good measure, also had an affair with. She took the boy back to Toulouse and two or three years later emigrated to Argentina.
Gardel died in an airplane crash in 1935 at the height of his career
The Argentine version is that Gardel was born in France but was brought to Argentina as a young boy where, as a resident of Buenos Aires and not Montevideo, he rose to become an Argentine, not a Uruguayan, tango legend.
"Who cares where he was born?" I hear you ask. "Just listen to the music and watch where you flick that tango heel."
But this dispute goes to the heart of Argentine and Uruguayan national identity.
Tango is not just a style of music and dance - it is the beat to which both nations evolved from their immigrant roots. It matters.
There is a commission in the town of Tacuarembo dedicated to proving that Gardel was Uruguayan.
Four years ago an Argentine judge refused a Uruguayan request to have Gardel's remains disinterred for DNA testing to prove links with alleged Uruguayan relatives.
And now an Argentine study group has sent a delegation to Uruguay with evidence that Gardel was not born there. They want the issue discussed in the Uruguayan Parliament.
Tango was born at the end of the 19th Century in the brothels and bars of Buenos Aires when men, in simulated knife fights, danced with other men.
Because of those roots, tango was for a long time associated with sleaze - and it was in this world that Carlos Gardel grew up - a notorious womaniser who, it has been strongly rumoured but never proved, served a prison sentence before he became famous.
Because of this shady past, Gardel was decidedly ambiguous when questioned about his early years. One Argentine theory is that he made up his Uruguayan background to confuse his identity and cover up his prison record.
And how could a man, ask the Argentines, who sang with such passion about his beloved Buenos Aires, be Uruguayan?
Looking at photographs of Gardel, with his cheeky smile and trilby hat set at a rakish angle, I cannot help but think that he deliberately sowed the seeds of this controversy.
And, more than 70 years after his tragic demise, is quietly relishing the debate, wherever it is that tango singers go when they die.
From Our Own Correspondent was broadcast on Saturday, 16 August, 2008 at 1130 BST on BBC Radio 4. Please check the programme schedules for World Service transmission times.