It depends on how far back national Identity and its connection to history goes back

For China it is over 4,000 years

For the UK it's the 9th century from the time of Alfred the Great and the Anglo-Saxon kings of England

Or alternatively in regards to continuity the Norman conquest in the 11th century

For France it's a different story because it severed its connection to its past when chopping off the head of Louis XVi of France in 1793

Since then France has had 5 French republics, 2 French Empires and the monarchy restored twice