From Lakota America: A New History of Indigenous Power, by Pekka Hämäläinen (The Lamar Series in Western History; Yale U. Press, 2019), Kindle pp. 267-268:
The United States emerged from the catastrophic war not as a nation but as an empire. The rebelling states remained on maps as before the war, but in reality they were captive territories under military occupation and governance. Acting without any political precedent—how does a failed republican state reunite?—the federal government set out to reconstruct the South after its own image. This was the era of authoritative government agents tasked to impose industrial capitalism, yeoman farming, democracy, and Christian civilization on a vast canvas. “We are to have the charge of this continent,” declared the Reverend Henry Ward Beecher. “This continent is to be from this time forth governed by Northern men, with Northern ideas, and with a Northern gospel.” It was a formula for a comprehensive reconstruction that would simultaneously target both the Southerners and Native Americans. There would two reconstructions, one focused on the rebuilding and reforming the South, the other on pacifying the Indigenous West.
The reconstruction of Indigenous America had to start with the rebellious Lakotas and their allies, and the first challenge was to agree how to achieve it. Several generals insisted that force alone would make Indians give up raiding and settle down, but many eastern politicians and philanthropists, sickened by the Sand Creek massacre, argued that moral education was the only justifiable course. Congress sided with the humanitarians and appointed, in March 1865, Senator James R. Doolittle, a staunch Baptist and patriot, to lead a joint special committee to investigate the state of Indian-white affairs in the West. It authorized commissions to negotiate new treaties with the plains tribes, including the Sioux. The Sioux commission was headed by Newton Edmunds, governor of the Dakota Territory, who was desperate to put an end to the Indian wars that hindered white settlement in his territory, blocking its path to statehood. Pressure came also from Nebraska to the south, where the construction of the Union Pacific Railroad was poised to start in Omaha, making Lakota appeasement a matter of national importance.
Repeatedly humbled by nomad warriors over the years, generals denounced the congressional version of the Indigenous reconstruction as lily-livered and misguided. Sully and Sibley wanted to keep the pressure on the Lakotas, and Pope, in charge of military operations in the Dakota Territory, was deeply cynical of the logic of offering new treaties to the plains tribes. How will they understand treaties and annuities he asked, if “the violation of former treaties and the murder of whites are to be thus compensated?” As he saw it, treaties actually boosted Lakota raids. “It is a common saying with the Sioux, that whenever they are poor, and need powder and lead, they have only to go down to the overland routes and murder a few white men, and they will have a treaty to supply their wants.” Pope was not entirely wrong. Since the opening of the Oregon Trail in the mid-1840s, Lakotas had tolerated overland traffic because it yielded resources, whether secured through trading, raiding, extortion, or, as Pope now claimed, through treaty goods.