It is an interesting question whether the French Canadians' efforts to create a separate country, in the late 1970's, did more harm to the French Canadians and Canada than the second emancipation of American blacks in the 1960’s did to the black community and America.
The French Canadians made a strong effort to form a separate French country in Canada. Primarily focused on Montréal. The consequence was that most national corporations pulled out of Québec and many smaller businesses did the same. Since the early 1980's Québec has been the recipient of massive welfare support from the rest of Canada to make up for the lost businesses. The French Canadians have become parasites on the larger society. There is no end in sight.
Black Americans in the late 1960s and well into the 1980s were burning their own neighborhoods in large cities. With vast national welfare resources available, the black community led the rest of the nation in creating children with only a mother.
The consequence, over one generation, was the rapid increase in crime in the black community to the point where blacks commit five times the number of crimes of other Americans and commit roughly half of all crimes in America.
Moreover the black community, despite massive federal and state aid for education, has created the first large modern illiterate and innumerate population.
The combination of crime and unemployment in the black community has created a serious and dangerous underclass that shows no prospect of improvement in the future.
I am not a dispassionate outside observer, but because of the high education and modest crime of the French Canadians, I think black America has done far more damage to America than have the French Canadians to Canada.