Quoting azade:

I'll put everything I have the reason for this tendency is the lack of integration of immigrants from different cultural backgrounds.

Quoting thehandsom:

I dont know where that passage has taken from but I dont think it bears the truth.
Nationalism is a dying ideology. It has been used just after the industrial revolution to keep people in nation states.
Of course, before that there was agricultural revolution and religions to bind people.
Specially in EU, after two wars, religion and nationalism have been getting less and less important.
Rest of the world will follow the same pattern eventually.