Multiculturalism was never intended by God....He made distinctions for a reason....otherwise a it's man made endeavor to attempt to unite varying cultures...and it will not work as they intend it to.
1. "those from... Africa nations do not assimilate well in Western nations overall" -- that's not true for Christian Africans from Africa who are hard working and integrate -- they speak fluent French or English and merge well. Even the Eritreans who head to Italy
2. "... because most are Islamic" -- those from Moslem countries yes, but the boat refugees to Europe are at least 50% Christian -- from sub-Saharan nations or from Eritrea or Syrian Christians etc.
3. "Multiculturalism was never intended by God.." -- sorry, He definitely DID intend it, that's why there are multiple cultures across the world. Christianity spread among myriad cultures and that was good. Multi-culturalism in which people respect each other's Christian (or Zoroastrian or Hindu or Buddhist -- but not Moslem (more on that later)) cultures is GOOD
Islam is NOT a culture, it is a civilisational virus, so all of the above statements are not relevant to Islam
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Look at England even -- it has strong cultural differences between Yorkshire and Cornwall and Sussex and Essex. even today