You can see in this table the degree of genetic diversity for each population.
The 'self' column shows the number of shared IBD ("identical by descent") blocks with other individuals of that country. The 'other' column compares IBD blocks with other countries. The higher the value the more recent the common shared ancestry. The Italians have the lowest self value (0.6), followed by the French (0.7) then the Belgians, Germans and Swiss (all 1.1). These are Europe's most genetically diverse populations according to this study. This coroborates my own
research on surname diversity, which I found to be the highest in Italy, then France, then Belgium.
The most homogeneous by far are the Albanians (14.5) and the Kosovars (9.9), followed by the Slovenes (5.0), the Russians (4.3), the Poles (3.8), and other Slavic peoples. It means that the Albanian and the Kosovan populations expanded quite recently from a much smaller source population.
However the Albanians, Kosovars and Montenegrins have the highest percentage of shared IBD blocks with the rest of Europe. This is surprising considering the very different Y-DNA lineages found among these populations, notably the very high frequencies of E-V13 and J2b. Perhaps it is the result of the Balkans being the starting point of the Neolithic diffusion on the one side, and that the region was also invaded by all kinds of Europeans (Celts, Greeks, Goths, Slavs) who all left their genetic print in the Balkans. So it works both ways. All Europeans have a bit of Albanian, but all Albanians also have a bit of other Europeans in them.
The Spaniards, the Cypriots, and oddly enough also the Macedonians appear to be the most isolated populations from the rest of Europe. They are closely followed by the French, Swiss, Italians, Portuguese and Turks.
The study also supports a recent Slavic expansion, which not only includes the northern Slavs, but also the southern Slavs (Serbs, Croatians, Slovenes, Bulgars) who all share a lot of IBD blocks with other Slavic populations. That
could mean that the Eastern European Y-haplogroup I2a1b-Din was spread around the Balkans during the Slavic migrations, and was not present in the region since the Mesolithic, Neolithic or even Bronze Age.