This is a function of the genetic and cultural distances between the host and minority peoples. The smaller the distance(s), the greater the percentage of said minorities that can co-exist peacefully and prosperously with the dominant host population.
Take Chinese society for example. Officially the country has 56 recognized ethnicities, with the Han being the dominant one at ~90%, followed by 55 minorites of varying sizes. With the exception of a few miniscule ethnic groups such as the Russians, Tatars & Tajiks, the rest at least all still belong to the Mongoloid race; the Uyghurs, a quite large minority is an exception to this exception, and will be further explained below. Additionally many of the more populous ethnic minority groups have become so assimilated/integrated into the mainstream Han society that they don't even have a separate language in use, such as the Manchus, the Huis, etc. The Hui people, a predominantly Muslim ethnic group, also provide a good contrast to the Muslim Uyghurs, who are a Caucasoid and Mongoloid admixed population, mentioned earlier. The Huis are peaceful, and well integrated (though not fully assimilated, as they still keep their own customs), whereas the Uyghurs represent a constant terrorist and separatist threat; many go to join Islamic extremist groups in the Middle East to train, then return to China to further their agenda via violence. It's not a coincidence that the former is ~93% Han in their ancestry (the remaining coming from West Eurasian traders who have traveled the Silk Road throughout the centuries), and the latter is only ~50% East Asian in ancestry.