One of the diaries I wrote in my US to 1865 series discussed the Indian Removal Act of 1830. In it, I cited Ojibwa's diary on the same subject, and I'd like to remind you of what we agreed on as the central idea behind the Act, in Ojibwa's words:
Removal was essentially a racially motivated idea. In the nineteenth century, most Americans tended to view Indians in racial terms and ignored cultural differences. They viewed all Indians as the same.
So now we're in the Gilded Age. Many of the Indians who were relocated from the East lived in Indian Country (present-day Oklahoma), but many more were native to the country West of the Mississippi, and these Indians were fighting to stay on the lands their ancestors had lived on for centuries. They had no help from the federal government; in fact, the government continued to pass measures that totally disregarded the fact that real people occupied the lands that the government was giving away. It's difficult to teach this without showing a great deal of irritation, so follow me below the Great Orange Basket as I take aim at a very large and diffuse target.
In order to understand the post-civil war developments, I have to go back to the original Indian Removal Act. As you of course remember, the objective of Andrew Jackson's Indian Removal Act was a type of segregation: move the natives west of the Mississippi and keep the Euro-Americans east of the Mississippi. But the treaties also allowed people to stay where they were, and now I get to define a term that was used a LOT in discussing these developments: allotment in severalty. Allotment was used to reconcile the Indians who didn't want to go to Indian Territory; those natives could take an allotment of land as private property. In severalty simply meant that land was allotted to more than one member of a given tribe. Nice in theory. Enabled land speculators to perpetrate land fraud. Discredited allotment throughout the 1840s.
For all his myriad faults, Jackson couldn't have foreseen that the United States would conclude a war with Mexico by appropriating half its territory, nor that gold would be discovered in the land appropriated by Mexico. He might have understood that the expansion of the railroads would disrupt his theory, but I doubt he would have cared. If you've forgotten, here's what the Treaty of Guadalupe Hidalgo did.

Jackson, however, died in 1845. The opening salvo of railroad expansion caused enough problems for Euro-Americans, given the fact that it was Steven Douglas's Kansas-Nebraska Act (1854) which started what we should really call a war between slaveholders and free-staters in Kansas but which we don't because the slaveholders started it. Perhaps not amazingly, Indian removal went on too. The Commissioner of Indian Affairs, George Manypenny renewed the practice of allotment to remove Indians from areas where Euro-Americans were settling -- and several treaties that removed Indians in conjunction with the Kansas-Nebraska Act had allotment provisions. More land fraud, this time on the Great Plains. And Manypenny will turn out to have been one of the GOOD guys.
The problem this time was that there was no large area West of the Mississippi to house the tribes that "had to be" relocated, because here we are West of the Mississippi. Allotment now became an award for acculturation, as the objective of the government became a renewed push for the "civilization" of the tribes -- we know how well that worked for the Cherokees, yes? There's another word for this: assimilation, or bringing the native peoples involved out of savagery to civilization. They would do this with white people too later in the century, but with these white people there was no land involved.
President Grant was VERY interested in this process, and here, spare us all from the well-meaning. He really didn't want the Army to deal with the Indians, thinking this would be an unnecessary provocation, so, in 1869, he gave Quaker and Protestant (yes they separated these out) missionaries control over reservation life, because they weren't the army and set up a civilian advisory panel to direct the process of civilization. This panel recommended that the sooner the native inhabitants of the West accepted the idea of private property, the better we'd all be. Tone-deaf? Well, of course. Then, in 1871, Congress decided that the identification of Indians as foreign nations with whom the government made treaties (see Worcester v Georgia [1832]) was ridiculous and passed a bill stating that the government would no longer make treaties with groups of Indians.
No treaties? So now what? The Dawes Severalty Act, also referred to as the General Allotment Act, of 1887 was the culmination of sixteen years of government attempts to make this iteration of the civilization process work, and to thus remove even more Indians from areas where Euro-Americans wanted to live, or wanted to exploit for profit. Why did it take sixteen years? It's like gun control and Newtown, and, as we know, the Army (see George Armstrong Custer) hadn't stayed out of it.
The event involved the Ponca Indians. (This is George Catlin's painting of Hongs-káy-dee, Great Chief, Son of The Smoke [1832]. Note to Ojibwa: If you haven't' discussed Catlin yet, I'll be happy to!)
A treaty signed by the Sioux in 1868 included some land that had been given to the Poncas, also by treaty, in 1865. The Sioux didn't want the Poncas to live on their reservation. They petitioned the government, and, in 1877, the government deported the Poncas, against their will, to Indian Territory, where many of them died from diseases. When, two years later, their chief Standing Bear tried to lead them back to Nebraska, the army stepped in to prevent this.
This aroused the Boston Indian Citizenship Association, whose members included Senator Henry Dawes of Massachusetts
and the novelist Helen Hunt Jackson, the author of
Ramona. They concluded that severalty, in this case the allotment to each individual Indian of title to a fixed number of acres of the land held by the entire tribe, was the best solution to the question of what to do with Indian lands. A bill was written. The Indian Affairs committee of the House disagreed on its expedience and morality. The five "civilized" tribes (the descendents of the survivors of the Cherokee, Chickasaw, Choctaw, Creek and Seminole removal) objected to the breakup of their tribal holdings. The debate went on for six years, and I really wouldn't go into detail on this except for the fact that the details of the bill were not hashed out in Congress. They were discussed here

at the annual Lake Mohonk (NY) Conference in Behalf of the Civilization and Legal Protection of the Indians of the United States. By philanthropists and professional anthropologists. Between 1883 and 1885. As if Congress decided that CPAC was a more appropriate venue to discuss DOMA and ENDA than Congress itself.
The bill at this point was based on the Homestead Act of 1861. Each adult who accepted allotment would get 160 acres, the amount allocated to farmers. It didn't matter if the individual Indian wanted to be a trader instead of a farmer, because the assumption, just as it had been when George Washington and Henry Knox had floated it to the tribes 80 years previously, was that the Indian would want to become a farmer. The climactic debate on the bill happened at Lake Mohonk in 1885, where one Reverend Dr. Lyman Abbott, who admitted that he had never been on an Indian reservation, insisted that the reservation system had to be ended over the objections of people like Senator Dawes. Here's the Secretary of the Interior, Lucius Quintus Cincinnatus Lamar of Mississipi, to Dawes in November 1885
It would hurt no interest in the country to [break up the reservations], but it would, by destroying the Indians, violate the moral obligation under which this nation rests to protect the Indians, to ameliorate their condition, and to spare no effort nor expense nor sacrifice to elevate them to a position fitting them to be citizens of the United States.
"Fitting them to be citizens?" Surely the Fourteenth Amendment . . . but no. In
Elk v Wilkins (1884) the Supreme Court,
citing Roger Taney in Dred Scott, said no, no more than the son of a foreign diplomat who was born here was.
Voila, a carrot for the supporters of allocation. The reformers added a clause that said that your reward for accepting allocation would be, yes, being declared a citizen of the United States. And what would happen to the unallocated lands of a reservation after the allocation was complete? They would revert to the United States. Presto, no more reservation, and by implication, no more tribe.
So here's the bill. No need to copy all of it here, since the discussion has already covered most of what it does. But here's a clause from Section V
And provided further, That at any time after lands have been allotted to all the Indians of any tribe as herein provided, or sooner if in the opinion of the President it shall be for the best interests of said tribe, it shall be lawful for the Secretary of the Interior to negotiate with such Indian tribe for the purchase and release by said tribe, in conformity with the treaty or statute under which such reservation is held, of such portions of its reservation not allotted as such tribe shall, from time to time, consent to sell, on such terms and conditions as shall be considered just and equitable between the United States and said tribe of Indians, which purchase shall not be complete until ratified by Congress, and the form and manner of executing such release prescribed by Congress: Provided however, That all lands adapted to agriculture, with or without irrigation so sold or released to the United States by any Indian tribe shall be held by the United States for the sale purpose of securing homes to actual settlers and shall be disposed of by the United States to actual and bona fide settlers only tracts not exceding one hundred and sixty acres to any one person, on such terms as Congress shall prescribe, subject to grants which Congress may make in aid of education:
and here's Section X
That nothing in this act contained shall be so canstrued to affect the right and power of Congress to grant the right of way through any lands granted to an Indian, or a tribe of Indians, for railroads or other highways, or telegraph lines, for the public use, or condemn such lands to public uses, upon making just compensation.
Indian removal under another name, pure and simple.
And Secretary Manypenny? Here he is in a letter to Dawes, October 20, 1885:
Had I known then, as I know now, what would result from those treaties, I would be compelled to admit that I had committed a high crime
Sources: Emily Greenwald,
Reconfiguring the Reservation The Nez Perces, Jicarilla Apaches, and the Dawes Act
Wilcomb E. Washburn,
The Assault on Indian Tribalism: The General Allotment Law
UPDATE: I'm leaving to do some research and to attend a meetup of the LA Kossacks in about 90 minutes, and I don't expect to be back until 8-9 PM Eastern (I'm not taking anything wireless with me). I'll respond to your comments when I get back.