If the Soviet Union was the “The Prisonhouse of Nations,” then the Caucasus region must be the refuge of the languages. Not only is this region linguistically diverse on a fine-grained scale, but there are multiple broader language families which are found nowhere else in the world. The widespread Indo-European languages are represented by Armenians, Greeks, and Iranians. The similarly expansive Altaic languages are represented by the Turkic dialects. But in addition to these well known groups which span Eurasia there are the Northwest Caucasian, Northeast Caucasian, and Kartvelian, families. These have only a local distribution despite their distinctiveness.
On the one hand we probably shouldn’t be that surprised by the prominence of small and diverse language families in this rugged region between Russia and the Near East. Mountains often serve as the last refuges of peoples and cultures being submerged elsewhere. For example, in the mountains of northern Pakistan you have the linguistic isolate of Burusho, which has no known affinity with other languages. Likely it once had relatives, but they were assimilated, leaving only this last representative isolated in its alpine fastness. The once extensive Sogdian dialects (Sodgian was once the lingua franca between Iran and China) are now only represented by Yaghnobi, which persists in an isolated river valley in Tajikistan. How the mighty have fallen! But the mountains are always the last fortresses to succumb.
But the Caucasus are peculiar for another reason: they’re so close to the “action” of history. In fact, history as we know it started relatively near the Caucasus, to the south on the Mesopotamian plain ~5,000 years ago. Therefore we have shadows and glimmers of what occurred on the south Caucasian fringe early on, such as the rise and fall of the kingdom of Urartu ~3,000 years ago. The ancient ancestors of the Georgians even show up in Greek myth, as the Colchis of Medea. And this was a busy part of the world. Hittite, Greek, Roman, and Arab, came and went. The rise of Turkic resulted in the marginalization of many of its predecessors. Some scholars even argue that the Indo-European and Semitic languages families issue from the north and south fringes of the Fertile Crescent, respectively. And it isn’t as if history has skirted the Caucasians. The Georgians faced the brunt of the Mongol armies, while the Circassians have famously been present across the greater Middle East as soldiers and slaves.