The motivation that sent the Washburn party into the Yellowstone region in 1870 was largely an outgrowth of two unrelated events of the previous year—the effort to activate the Northern Pacific Railway project, and the struggle over the governorship of the Territory of Montana. Thus, it is necessary to consider these peripheral events before continuing with the definitive exploration of the Yellowstone wilderness.
An act of Congress chartering the Northern Pacific Railway was signed into law by President Abraham Lincoln on July 2, 1864, but the enterprise remained a paper venture (in which the resources provided by the stockholders were consumed without apparent benefit) through 1869. In that year, the board of directors, made desperate by the knowledge, that they would lose both the charter and the munificent land-grant which accompanied it if the prescribed amount of line was not in operation by the end of 1870, turned to the investment house of Jay Cooke & Co., for help. 
This marriage of convenience was not consummated at once, for neither group trusted the other. The “old NP faction,” headed by J. Gregory Smith—generally addressed as “Governor”—talked of “keeping things in our hands,” because “Jay knows nothing of RR Building,”  and they moved their secretary, the astute and crafty Samuel Wilkeson into an office in New York City, from whence he could advise the Cooke people and divine something of their maneuverings from the city’s financial gossip.
The Cooke group, which also included Henry D. Cooke, Pitt Cooke, William G. Moorhead, H. C. Fahnstock, Edward Dodge, John W. Sexton, and George C. Thomas, was not as poorly informed as their distrustful confederates presumed, for they had the excellent counsel of A. B. Nettleton (Cooke’s office manager) who, as a general officer in the Civil War, had built and operated many of the railroads which gave the North its logistical superiority in that struggle. These financiers were fearful that the railroaders would waste construction funds in contractual arrangements with cronies, and that the lands available under the railroad’s grant—the real security for its bond issues—would be wasted.
The two groups sparred over terms during the remainder of 1869, but finally reached an agreement which gave the banking house representation on the Northern Pacific board and a controlling interest in the railroad’s stock in return for an immediate advance of $5 million.  That funding allowed construction to begin on the Minnesota shore of Lake Superior, February 15, 1870, on ground thawed with bonfires. 
The enterprise thus launched had supporters in and out of the Government, from House Speaker James G. Blaine to Henry Ward Beecher, most of whom had such compelling reasons for their interest as the ownership of Northern Pacific stock or acceptance of gratuities and “fees”; and there were would-bc-friends in the West who sought to ingratiate themselves with the enterprise for various opportunistic reasons. Some of the latter found a measure of acceptance with the Cooke faction, but to the railroaders they were nearly all anathema—a viewpoint which is explained by the following excerpt:
. . . Governor Ashley and a rich man from Toledo, Ohio have put squatters on our pet, our choice, location at Thompson Falls. The choisest and best land on our line of reconnaissance within a year will be gone. 
One westerner—a term intended only to designate those men whose sphere of activity was Minnesota and Montana, rather than the financial centers of the East—who nearly made the grade with the old Northern Pacific group was the editor of the Helena Herald. He was introduced to President Smith in these glowing terms penned by Samuel Wilkeson:
Robert E. Fiske—the bearer—is the Republican Editor of Montana—and the Republican brains & heart of that future mighty State.
He loves our Road—Our Road should love & cherish him.
Every syllable of his advice is worth heeding. 
But he was not heeded; rather, he was soon considered a “wicked or mean” man, on the advice of one whose contacts were Montana Democrats.  The railroaders thus turned their backs on a group which could have been formed into a powerful ally.
The Cooke people were not so disdainful of westerners. They made use of Governor Ashley, even after his true character was all too clear, and they leaned heavily on William R. Marshall, the Governor of Minnesota (1866-70).  Quite probably, the latter arrangement included Marshall’s brother-in-law, James W. Taylor,  that enthusiastic apostle of American economic penetration of the Canadian prairies (which he presumed would eventuate as a “Northern Texas,” wrested from British rule by American citizens), but what is important here is the influence of these men—particularly Taylor—on a younger brother-in-law, Nathaniel Pitt Langford. Of this influence, one biographer says:
Langford’s story in Montana’s early history is well known. That he was an “agent of an agent” there seems little doubt. Indirectly he was an observer and a protagonist for the northern railroad routes. During his time in Montana he seems always to be acting as he would expect Taylor to act and speak if he were there on the scene. His interest in getting Virginia City’s gold safely to Washington, and in securing the resources of the area for the Union seem honestly to have been his conscious effort. . . . That N. P. Langford was not James Wicks Taylor is just as obvious, but he did his best. 
Taylor, of course, was the source of Langford’s political leverage. As a former law partner of Salmon P. Chase (with whom he enjoyed a close ideological rapport), Taylor was able to obtain the position of Collector of Internal Revenue for Montana Territory for his protégé, and he nearly managed the governorship of the territory for him in 1869.  Following that defeat Langford gradually became involved in the familial interest—the Northern Pacific Railroad.
Langford, whose diary indicates that he left Montana on October 26, 1869,  showed up at the New York office of the Northern Pacific on March 18, 1870. Secretary Wilkeson reported this visit to President Smith in a confidential letter, as follows:
A smart fellow, anciently a bookkeeper—during the war detailed as quartermaster to an expedition from Minnesota overland to Fort Benton and thence through Cadottes, the Deer Lodge & other passes, came in yesterday to get employment. Before he left he asked me if Vibbard & Co. were to have the contract of supplying the Northern Road—and said that he was told by that house the day preceding that they expected to have the contract. Canfield Probably told you of my conversation with Vibbard six months ago on the subject of that contract. I was told then that I was to have an interest in it. 
An item which appeared in the Philadelphia Press the day following this visit is so patent a re-statement of James W. Taylor’s views that Langford may be suspected of supplying the material to enhance the sale-value of his knowledge of Montana and the northern railroad route.  But he was displaying his wares in a poor market, for the railroad could not afford a salary for its secretary at that time.
From April 4 to May 11, Langford accompanied brother-in-law Marshall on a trip to Fort Garry, in British territory. By the middle of the month, Marshall was advocating the construction of a White Cloud-Pembina line to tap the rich Red River Valley (He made several attempts to communicate his enthusiasm for that route to President Smith ). As June opened, Langford was in Washington, D.C., in a further attempt to contact Smith. 
Though unable to reach the autocrat of the Northern Pacific Railroad, Langford did manage a meeting with Jay Cooke 2 days later. This is noted in Langford’s diary as follows:
June 4, 1870, Sat. Met Jay Cooke [illegible] and went to Ogontz  with Mr. Cook.
June 5, 1870, Sun. Spent day with Mr. Cook.
What their common interest was remains a matter for speculation, but the directness with which Langford returned to Montana Territory and began organizing the 1870 exploring party hints that the Yellowstone region figured in the conversations. Regardless, Langford had found a place as one of the corps of lecturers who were to expedite the sale of Northern Pacific Railway bonds by popularizing the region through which the line was to be built.