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 <WSD>unit</WSD> until long 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:  an organization regarded as part of a larger social group