It is often remarked how bad the human tribal nature is. The following passage from Nassim Taleb's seems to illustrate the point. Or can we see something contrary to the common wisdon there?

For more than a millennium the eastern Mediterranean seaboard called [Mount Lebanon] had been able to accommodate at least a dozen different sects, ethnicities, and beliefs -- it worked like magic. [The] Levantine cities were mercantile in nature; people dealt with one another according to a clear protocol, preserving a peace conducive to commerce, and they socialized quite a bit across communities. This millennium of peace was interrupted only by small occasional friction within Moslem and Christian communities, rarely between Christians and Moslems. [The] mosaic of cultures and religions there was deemed an example of coexistence: Christians of all varieties (Maronites, Armenians, Greco-Syrian Byzantine Orthodox, even Byzantine Catholic, in addition to the few Roman Catholics left over from the Crusades); Moslems (Shiite and Sunni); Druzes; and a few Jews. It was taken for granted that people learned to be tolerant there [...]

Both sides of my family came from the Greco-Syrian community... [We] originate from the olive-growing area at the base of Mount Lebanon -- we chased the Maronite Christians into the mountains in the famous battle of Amioun, my ancestral village. Since the Arab invasion in the seventh century, we had been living in mercantile peace with the Moslems, with only some occasional harassment by the Lebanese Maronite Christians from the mountains. By some (literally) Byzantine arrangement between the Arab rulers and the Byzantine emperors, we managed to pay taxes to both sides and get protection from both. We thus managed to live in peace for more than a millennium almost devoid of bloodshed: our last true problem was the later troublemaking crusaders, not the Moslem Arabs [...]

By any standard the country called Lebanon, to which we found ourselves suddenly incorporated after the fall of the Ottoman Empire, in the early twentieth century, appeared to be a stable paradise; it was also cut in a way to be predominantly Christian. [The] Christians convinced themselves that they were at the origin and center of what is loosely called Western culture yet with a window on the East. [...]

The Lebanese "paradise" suddenly evaporated, after a few bullets and mortar shells. [In 1975,] after close to thirteen centuries of remarkable ethnic coexistence, a Black Swan, coming out of nowhere, transformed the place from heaven to hell. A fierce civil war began between Christians and Moslems, including the Palestinian refugees who took the Moslem side. It was brutal, since the combat zones were in the center of the town and most of the fighting took place in residential areas... [The] conflict lasted more than a decade and a half. [...]

Aside from the physical destruction (which turned out to be easy to reverse with a few motivated contractors, bribed politicians, and naïve bondholders), the war removed much of the crust of sophistication that had made the Levantine cities a continuous center of great intellectual refinement for three thousand years. Christians had been leaving the area since Ottoman times--those who moved to the West took Western first names and melded in. Their exodus accelerated. The number of cultured people dropped below some critical level. Suddenly the place became a vacuum [...]

Quite a remarkable transition - yet probably not the only example of long piece suddenly gone. On the other hand, knowing what is happening in the Middle East in the last decades, can we imagine that people there were not that stupidly violent for much longer times? That millennium-long Levantine peace is quite a reverse-time black swan from our perspective. What were the Levantines doing that whole millennium of piece, how did they manage their wicked human nature that peacefully for so long? What did force them to be so tribal again? Was it only differentials in birth rates? Or turning it around, what it takes to make a long-lasting peace?