The Russian Empire, the USSR (and Russia to lesser extent) were such examples. The Russian Empire included drastically different ethnicities (from Poland to Buryatia) and in some sense it was multicultural. However one can't say that those people co-existed peacefully and Russian metropolia had to wage wars against its colonies. Also, no one pretended that all cultures were equal and vaild, rich Christian Russians were the overlords.
The Soviets managed to integrate muslim, christian, and even buddhist republics even better, in many ways because they slipped into their inner workings at much deeper level than the Empire ever did. It demanded from national republics (new word for former colonies) to leave the middle ages behind and embrace papa Lenin. Imo it was quite successful, Armenians lived in Baku, Azeri lived in Armenia, Russians lived in Chechnya, Jews lived in Uzbekistan, muslim Tatars and Bashkirs were integrated and made secular. Soviet cinema showed people of various ethnicies and underlined that everyone was a friend of everyone as long they are all working class. Was the USSR multicultural, though? Yes and no. You could have retained your culture until the said culture was in line with the Party. Of course, anyone who refused integrate, faced the wall.
. Essentially they're trying to do what Switzerland did - create a fake nation out of multiple ethnicities.
Interesting, how in the USSR there was a term "soviet man" aka homo soveticus. It was artificial and fake and generally ended when the USSR gtfo-ed itself, leaving a rather vague term "Russian". Unlike in English, in Russian the word "Russian" have two differed meanings. Russian aka the citizen of the RF, and Russian aka a person of Russian ethnicity (white, slav, etc). As you can guess, those two are wildly different.
