While investigating on Albania, I kept finding peoples I never heard of before. Notwithstanding my vast ignorance, this was systematic to the point that I started investigating. Take a look at this map: it does not even reproduce all of the ethnic groups. The overabundance is so evident that this question is asked elsewhere on the internet (with no answer, spare that click for later). This website has a comprehensive list of ethnicity, but offers no answers. I was impressed reading:
According to the Roman historian Pliny, when the Romans came to the Caucasus, they needed 134 interpreters to deal with the jumble of languages they found. The 10th century Arab geographer and historian al-Azizi referred to the area as the “mountain of languages”. Today, this relatively small area (about the size of New England) is home not only to over 100 languages, but to four distinct language families that are indigenous and unique to the region: the Northwest Caucasian family, the Northeast Caucasian family, the Nakh family and the South Caucasian (or Kartvelian) family. In addition, several languages from families common elsewhere – Indo-European and Turkic – are spoken by various groups in the Caucasus region as well. Like the linguistic situation, the ethnic situation too presents a complex and highly mosaic picture, because ethnicity correlates closely, though not perfectly, as we shall see below, with the languages.
We know how several (hundreds?) migrations brought people from Central and East Asia towards Europe and the Middle East. Most of these people established their own rule over some land, but it seems to me that invaders either survived to date as an ethnic and/or cultural majority (Hungary, Turkey, Bulgaria, ...) or disappeared as a group - leaving genetic and/or cultural heritage to different degrees (Huns, Lombards, Vikings, ...).
However, when we look at the ethnic map of Europe, there is considerable less fragmentation than in the Caucasus only, especially if one considers the difference in overall extension and population, and that Europe itself contains a fair amount of impervious regions (Alps, Pyrenees, ...)
The question: why so many groups survived (at least culturally) in the Caucasus compared to nearby regions? I'm interested both in geographical reasons and in historical developments (e.g. national states vs empires, political fragmentation vs centralization, ...).