Here's the gist of what this Act is saying. (Bear with us; it's not pretty.)
The only way those stubborn Native Americans can survive is to break up the reservations and assimilate them into American society with a path to citizenship. The government will give them the chance to farm and own some reservation land privately—hands off, tribes—and they'll recognize the benefits of this more civilized way of life. And if there's any reservation land left over after allotting it to individuals, it's ours. For a fair price, of course.
And P.S. We can still run railroads through your new property it if we think it would be for the common good. This is a one-time offer, folks—call in the next fifteen minutes for your 160 acres.
The Dawes Act was all about laying the groundwork for eradicating and/or subjugating the Native American way of life, legally and in such a way as to conceal its intent.
Dawes really wanted what was best for the tribes; his Eurocentric perspective just made it impossible to think that Native American culture was as good as his.
The government needed some way of obtaining Native American land for all the white settlers that were heading west, while forcing the tribes to assimilate into American culture. They needed a way to do that without looking like bad guys. The Dawes Act, with its misleadingly philanthropic-sounding program of individual land allotments, was the answer.
First and foremost, the Dawes Act wanted to establish the fact that tribes were going to have to live on designated amounts of land within the reservations. This would not only force them to give up the prime farmlands to white settlers, but it would make it necessary for them to abandon their traditional, communal agricultural methods for the American/European farming model (i.e., for one's own personal profit).
Any land left over after this generous allotment was now available for the government to purchase from the Native Americans, conveniently opening up even more land for the people playing the real-life version of The Oregon Trail.
We're gonna break up the reservation land and give it to individual Native Americans in the hope that they'll become just like the rest of us and give up their primitive tribal ways in exchange for U.S. citizenship. If there's any land left, we'll be happy to take it off your hands. PS: members of the Five Civilized Tribes need not apply.