Ft. Clark was built in 1831 (by the Upper Missouri Outfit) next to the Mandan village Mih-tutta-hang-kush. The first steamer arrived in the Mandan villages in 1832 and heralded the acceleration of trade, more visitors, and more entrepreneurs heading upriver. The beaver trade slowed by 1832 as silk had replaced the skins in fashion

George Catlin arrived in the summer of 1832, and Karl Bodmer, with Prince Maximilian, was there during the winter of 1833-34. Fr. Nicolas Point drew sketches of the villages in 1847. Jesuit priest Pierre Jean DeSmet visited several times, and accompanied leaders of the three tribes to Fort Laramie treaty grounds in 1851. Swiss artist Rudolph Kurz sketched, painted, and worked as clerk in Forts Clark, Berthold, and Union in the late184o's and early '50's. Granville Stuart recorded his impressions as he passed through in 1866.

The fur trade was over by 1867, marked by the abandonment of Fort Union. The era had brought some technological advantages to the Indian and a slightly higher standard of living, but the price they paid was indeed exorbitant by any standard (Cash: 1974). Everything had changed, and much was lost.

Victims suffered horrifying symptoms, leaving disfigured corpses. The effects were staggering and demoralizing. There were no means to fight this enemy. Witnessing the ferocious all-consuming disease overwhelmed the Mandans physically and psychologically. Four Bears, the beloved Mandan chief and long-time friend of the whites, made a dramatic speech calling for vengeance. The reduced and grieving people were incapable of launching any kind of attack.

The Mandan were nearly lost, and abandoned their Knife River villages for refuge with the Hidatsa and Arikara camps. Eventually, in 1844, the bands joined the Hidatsa in a new village site on the east side of the Missouri, Like-a-fish-hook. This village became the permanent home of the two tribes and the beginnings of Fort Berthold. People struggled to maintain traditional lifeways and knowledge with so many leaders gone.

In early June of 1843, Audubon walked through prairie and ravines around Fort Clark. He observed:
"As we walked over the plain, we saw heaps of earth thrown up to cover the poor Mandans who died of the small-pox. These mounds in many instances appear to contain the remains of several bodes and, perched on the top, lies, pretty generally, the rotting skull of a Buffalo" (John James Audubon: 1897).

Small pox was the most dreaded epidemic, but many others were devastating as well: cholera, influenza, measles, and streptococcal infection. Rudolph Kurz recorded in his journal in 1851:

"August 29. Today old Gagnon...came back from a visit to the Arikara. He says eight people died there in one night from the same disease that is prevalent here and called cholera; the symptoms are violent cramps and vomiting, and usually death results in a few hours. Gagnon was guilty of a mad act in running his Arikara woman away from here to Fort Clarke; by so doing he spread the contagion in the Arikara village. Dorson thinks as I do, however, that cholera was brought in those bales of goods that we opened. Perhaps he welcomed the occasion that Gagnon's arrival afforded him to throw blame on the opposition. Gagnon had to make his escape by night when he realized the results of his imprudent act. The Arikara have also abandoned their village for the most part and are seeking another distant location" (Kurz: 1969).

G. K. Warren was on reconnaissance for the Corps of Topographical Engineers in Dakota and Nebraska Territories when he filed this report in 1857:

"The Mandans live in a village, six miles above Fort Clark, in the same manner as the Gros Ventres. They seem to be the last remnant of a distinct tribe from any of those around them. They have, through the agency of the small-pox, rapidly diminished since they were visited by Lewis and Clark, and now number about 250 souls. They live in constant dread of the diseases which white men have been at times introducing among them, and the main and oft-repeated request which they made to the Indian agent when I was there in July, 1856, was that he would keep sick white men away. When I returned there in September, and saw them again a victim of that scourge, the small-pox, brought among them that year by the steamboat of the rival company to the American Fur Company, and saw the despair depicted on every countenance, it made me feel heart-sick to think what wrongs these poor savages have suffered from the cupidity of my own race. The authors of this calamity, which visited all the tribes in this region, are fully exposed in the report of the Indian agent, Colonel Vaughan, in 1856-'57…

"These three little bands, the Gros Ventres, Mandans, and Rees, are fast dwindling away. They never can work much harm to the whites, and their mode of life at a fixed abode requires them to be peaceful. They exist now rather by sufferance of the Dakotas than by their own power, for the Dakotas could soon destroy them if they chose, as they did the villages of the Pawnees, on the Loup Fork, in about the year 1836. The Dakotas find it convenient for themselves to permit the existence of these villages, as their produce of corn, &c., forms a valuable commodity of trade between them" (Warren: 1857).

Dr. Ferdinand Hayden, a scientist accompanying the Warren expedition, observed in 1855:

"When the survivors had rallied and recovered, they left the village at the fort, and took up their residence in the other cabins, a few miles above. Here some attempt was made to reorganize their social system, but the race could only be propagated by intermarriage without regard to relationship, unless closely allied. To this they were forced by circumstances. The disease had only left one family, here and there, and no choice was offered for new connections. However, they conformed as nearly as practicable to their customary laws...

"The Mandans at this time (1855) number about thirty-five or forty huts, perhaps nearly three hundred souls, raise corn, squashes, beans, &c., same as the Minnetarees and Arikaras, and hunt buffalo when these animals are near their village. The destroying and humbling effects of the disease referred to could not change their indomitable spirit of pride and independence. They will not join with the other nations near whom they reside, connect themselves with them by marriage, nor practise any customs but those of their ancestors. Their religious rites and ceremonies are preserved entire, and the system of self-inflicting tortures is practised at the present day. Being too few in number to form war-parties, they remain at home and defend themselves" (Hayden: 1862).

As the buffalo disappeared and other game diminished, the people became more dependent than ever on food subsidies. Health impacts were numerous.

"When subsisting for the most part on fresh meat, these Indians had the soundest gums and teeth; and no flesh when wounded healed more rapidly than theirs. Lately, however, since the increase in the consumption of bacon and flour among them, and the destruction of their game, there have been many cases of scurvy, a disease which was particularly fatal to them in the winter of 1868-'69; and a tendency to abscesses, to suppurative terminations of diseases, and to a sluggish condition of wounds, manifests itself. The quantities of fresh meat they are able to consume are enormous. Sometimes, after a day's hunt, the hunters will sit up all night cooking and eating"" (Matthews 1865).The faith of the Mandan in their sacred objects was unshaken by two severe smallpox epidemics. They speak of these epi­demics as unfortunate and explain the impotency of their rites to protect the tribe on the grounds that, when the original cere­monies were introduced into the tribe, the sacred beings made no promise of tribal immunity to the white man's diseases. They believe that the tribe would have been exterminated by their enemies subsequent to the last smallpox epidemic had the cere­monies been abandoned" (Bowers: 1965).