Without assimilation diversity/heterogeneity of stocks leads to factions divided along ethnic lines, and civil war eventually And western countries have given up on assimilation years ago, and even on integration Assimilation; immigrants adopt the culture (in the large sense; practices, habits, values, etc) of the majority, and become like them Integration; immigrants adopt all or parts of the culture of the majority, and the majority adopts all or part of the immigrants culture ... You resort to integration when assimilation isn't practicable basically, you look for a compromise (from a .gov standpoint). https://www.theoccidentalobserver.net/2017/02/24/aristotle-on-immigration-diversity-and-democracy/ Aristotle is greatly concerned with the preservation of civil peace in the city-state. One of the most common causes of “faction” and civil war, he says, was the unhappy consequences of unassimilated immigration and the consequent diversity. Aristotle’s prose is perfectly clear: Heterogeneity of stocks may lead to faction – at any rate until they have had time to assimilate. A city cannot be constituted from any chance collection of people, or in any chance period of time. Most of the cities which have admitted settlers, either at the time of their foundation or later, have been troubled by faction. For example, the Achaeans joined with settlers from Troezen in founding Sybaris, but expelled them when their own numbers increased; and this involved their city in a curse. At Thurii the Sybarites quarreled with the other settlers who had joined them in its colonization; they demanded special privileges, on the ground that they were the owners of the territory, and were driven out of the colony. At Byzantium the later settlers were detected in a conspiracy against the original colonists, and were expelled by force; and a similar expulsion befell the exiles from Chios who were admitted to Antissa by the original colonists. At Zancle, on the other hand, the original colonists were themselves expelled by the Samians whom they admitted. At Apollonia, on the Black Sea, factional conflict was caused by the introduction of new settlers; at Syracuse the conferring of civic rights on aliens and mercenaries, at the end of the period of the tyrants, led to sedition and civil war; and at Amphipolis the original citizens, after admitting Chalcidian colonists, were nearly all expelled by the colonists they had admitted. (1303A13) Thus, immigration of different peoples was a common source of conflict, often leading to civil war and concluding with the ethnic cleansing of either the native peoples or the invaders.