I think Tainter was laying out an historical process without the intention of giving us a date for American collapse. The separation of tribes doesn't necessarily require collapse, but would be facilitated by collapse. Separation of tribes can be accomplished on an individual basis by shunning other tribes and refusing to allow the members of other tribes into one's consciousness to the greatest extent possible. Sometimes ignoring works, and sometimes one must be rude.
Not many! But does he deserve reparations for simply being black, any more than some loser who didn't apply himself, flunked out of school and sells drugs now or robs people, then blames white people for his troubles? Even worse, do successful black people deserve anything because they "THINK" they haven't succeeded as far, because everyone around them is supposedly racist? They don't "deserve" anything, just like I don't deserve anything from the German govt for systematically wiping out 1/2 the Jews on the planet over 70 yrs ago. Any problems you face are your own, unless you suffered an accident completely out of your control. Hint: most people don't encounter life destroying accidents.