Allastriona asks Elvis, a Christian from Iran in exile in UK what he thinks is causing the downfall of The West.
Clearly the degree of multiculturalism is important, if it is similar culture like the differing European nations, it is fine, but if it is a huge difference in culture, it is guaranteed to clash.
Architecture is a good indication of the closeness between cultures. Like European architecture that went to USA with the British and Irish but had Italian and Greek influences and there was no problems with this.
However mixing very different cultures might seem novel and fun at first, when you talk about food and coffee table experiences, but when you go deeper there are serious clashes. This is mostly because many of these cultures are rooted in religion. This must be why the establishment is working so hard to destroy religions, to make it easier to create a One World Order.