Asabiyah
Perhaps Ibn Khaldun, the medieval Muslim scholar, can give us a hint. Ibn Khaldun spoke of asabiyah or social cohesion, as binding groups together through a common language, culture, and code of behavior. Asabiyah is what traditional societies possess, but which is broken down in urbanized society over a period of time. Ibn Khaldun famously suggested that rural and tribal peoples come down from the mountains to urban areas and three generations on, as they absorb the manners and values of urban life, they lose their special quality of social cohesion and become effete and therefore vulnerable to new invasions from the hills. This cyclical, if over-simplified, pattern held for centuries up to the advent of European colonialism. Even the disruptive force of European imperialism over the last two centuries did not break the cycle.
Look up Ibn Khaldun, Arnold Toynbee, Edward Gibbon, Sigmund Freud and others on the rise and fall of civilizations.
Look up Ibn Khaldun, Arnold Toynbee, Edward Gibbon, Sigmund Freud and others on the rise and fall of civilizations.