I believe you could take almost any college Sociology book and find what I told you in the above post.
Most people here are opposed to socialism, communism, and class warfare. They don't understand that adopting the terminology of class is opening the door to that. Read Sociology in Wikipedia if you think I am exaggerating. I believe that it is also explicitly unconstitutional, (I think the constitution bans all titles) though I have not had a chance to look that up.
Before 1964 certainly black Americans constituted a separate class. That is as far as I will go. Calling arbitary income groups classes os not only wrong, it is subversive.