IMO it never has and never will. We might get on with other ethnics, cultures and are friendly and amicable. However...all of us, everyone of us has a tribe! It's got to be IMO because of safety from way back.
Living together is a different thing, it can be irritating to some and each has his/her agenda. It will never...IMO work. The Africans are brash and loud and will not(why should they) change to live with their surroundings, that's for a start. The Brits will not adapt in their own country ...why should they, we have our history and past that has brought us up.
Anyone, in any country IMO stays with their upbringing and indoctrination....it's a given. If multiculturalism is forced upon any race, creed or inhabitants it will not be totally accepted because.....no one can help it.... It's life on this planet and will ever be.