I grew up in Montreal in the 50s and 60s in two different neighbourhoods and never even experienced that kind of mild, childish verbal jousting.  We just lived parallel lives that rarely  intersected, except for a few bilingual francophones going back and forth between groups. That was real "biculturalism", and it was not a good thing.

But no one ever heard of ethnically-based gangs with real violence involving knives, guns, etc.

There were different ethnicities, who spoke different languages at home, went to different religious places of worship, and ate different foods, but those were minor differences, everyone shared a basic common culture which we would now would call Judeo- Christian.