Sentence:  Nor have we remembered that in the melting pot of America the hundreds of isolated and semi isolated ethnic , regional and occupational groups did not fuse into a homogeneous national unit until <WSD>long</WSD> after education and industrialization had caused them to cast oral tradition aside as a means of carrying culturally significant material . 
Meaning of the word marked with <WSD> tags:  for an extended time or at a distant time