The Dawes Act of 1887: Questions

Why were certain tribes exempt from the Dawes Act?
How was one section =160 acres determined? What makes that the magic amount of land one person could live off of?
How do they prove that a deal is "in the best interests" of the Native Americans in question? It's pretty subjective, right?
What made the situation different in 1887 from earlier eras where the reservation strategy was satisfactory to the U.S. government?
Was the writing on the wall for the American Indians even before the Dawes Act? Things weren't exactly getting better for the tribes over the years.
Do you think there'd be any benefits for Native Americans to be assimilated into mainstream American culture?
Isn't American citizenship what all immigrants want? Oh, wait. They weren't immigrants. We were.
Why was the Dawes Act able to ignore the issue of tribal sovereignty?
Why couldn't we all just get along? (No…really. Why?)