PLOS has an interesting article which reports on the differentiation of European populations into northern and southern clusters, along with separability between various nationalities. Since until recently mate selection has been a function of distance and topography, and national borders also tended to be bounded by physical features (e.g., the Alps or the Pyrenees), it is no surprise that, on average, the French tend to cluster with other French. But, I do think quantification such as this is useful:
...most individual participants with southern European ancestry (Italian, Spanish, Portuguese, and Greek) have >85% membership in the "southern" population; and most northern, western, eastern, and central Europeans have >90% in the "northern" population group. Ashkenazi Jewish as well as Sephardic Jewish origin also showed >85% membership in the "southern" population....
As humans we are anthropocentric the biology and history of our own species has always fascinated us, and early in the 20th century there was a lot of scientific fantasy written about the Alpine, Nordic and Mediterranean races in Europe. Many of these "theories" were as entertaining and factual as the reality of the clans of Elves who left Middle Earth, the Vanyar, Noldar and Teleri. Today with the revolution in genomics and computing we can actually extract and analyze the structured information from the morpholoy and genetics.