The Great Plains contain what is referred to as the "nation's breadbasket," supplying the vast majority of various grains, particularly wheat, to the United States (as well as large amounts exported out of the country). In fact, Kansas is practically synonymous with "wheat." In addition to agriculture, livestock (especially cattle) have a long history in the region, mostly in the southern parts. Mineral and other nonliving resources are also abundant throughout the plains: gold, coal, petroleum, lead, zinc, uranium, and others.
Makes it seem like an ideal place for the westward expansion of America's manifest destiny during the nineteenth century. But that's not how it was seen.
Birth of the Myth
It was seen as "great"—but not the way one thinks of it now. The myth of the "Great American Desert" began with explorer Zebulon Pike who made expeditions through the region (following the Arkansas and Red Rivers) to the Rocky Mountains between 1805 and 1807. (The purpose was to discover the source of the Mississippi—which he erroneously identified—and to explore the Louisiana Purchase, much like Lewis and Clark did earlier.) He found a vast expanse of grasses on a treeless horizon with "soil generally dry and sandy, with gravel."
Little timber was to be found except along the banks of rivers and streams. It led him to "conclude, that this country never was timbered, as from the earliest age, the aridity of the soil having so few water courses running through it, and being principally dry in summer, has never afforded moisture sufficient to support the growth of timber."
Perhaps his clearest statement on the subject of these "internal deserts" comes from his Journal (published in 1810, all these quotes from there):
But here a barren soil, parched and dried up for eight months in the year, presents neither moisture nor nutrition sufficient, to nourish the timber. These vast plains of the western hemisphere, may become with time equally celebrated as the sandy deserts of Africa; for I saw in my route, in various places, tracts of many leagues, where the wind had thrown up the sand, in all the fanciful forms of the ocean's rolling wave, and on which not a speck of vegetable matter existed.
Accurate? In some ways. The amount of rainfall on the plains makes it considered to be "semiarid." Depending on what part of the region, average yearly rainfall runs between 10 and 25 inches, the southern and eastern plains getting the higher numbers—overall, the average is around 16 inches.
Many parts of the plains were subject to periodic or near drought because of weather patterns. While the severe drought(s) was not the sole factor in the dust bowl conditions during the 1930s (overplowing and overgrazing also contributed), it was a necessary component of what happened.
In other ways, not very accurate (forgetting that the climate doesn't really qualify it as a desert). It was more than adequate for the various bands of Indians that lived there—Pike calling the lands adjacent to the Arkansas as "the paradise (terrestrial) of our territories, for the wandering savages" (emphasis in original). There was abundant game and enough water if one stayed near rivers (Pike felt that only a limited population could be settled there).
But the plains were difficult, despite the millions of bison that migrated across the prairies, it is doubtful there was much Indian habitation there prior to the (re)introduction of the horse by the Spanish explorers. Survival on the plains made it necessary to have a more nomadic lifestyle, following the food sources (further, the difficulty of hunting bison without mounts would make it prohibitive).
Limits and Perpetuation of the Myth
All this was not considered a bad thing by Pike. In fact he felt it beneficial, as it would create a "restriction of our population to some certain limits, and thereby a continuation of the union. Our citizens being so prone to rambling and extending themselves." This limitation would keep settlement to the east of the Missouri/Mississippi and "leave the prairies [that are]incapable of cultivation to the wandering and aborigines of the country."
This Great American Desert would contain the nation and keep the "aborigines" in their place. Between 1819 and 1820, another expedition went through the region. Headed by Stephen Long, maps that he produced actually had the area titled as the "Great American Desert." His assessment was much the same as Pike, even as to the limiting factor of the plains:
[The Great Plains region] is almost wholly unfit for cultivation, and of course uninhabitable by a people depending upon agriculture for their subsistence. Although tracts of fertile land considerably extensive are occasionally met with, yet the scarcity of wood and water, almost uniformly prevalent, will prove an insuperable obstacle in the way of settling the country.
Continuing in eerily similar language, he thought it
may prove of infinite importance to the United States, inasmuch as it is calculated to serve as a barrier to prevent too great an extension of our population westward, and secure us against the machinations or incursions of an enemy
These views were accepted and held by many. Even expansionist senator Thomas Hart Benton "doubted whether an America that stretched across the plains to the Pacific could hold together politically" (Slotkin). On the other hand, he wasn't as skeptical about settlement as others.
In 1827, James Fenimore Cooper published the novel Prairie which perpetuated the myth, characterizing the plains as the desolate place it had become known as and having his intrepid pioneers beaten by its hardship. This conception of the plains was commonplace.
Indians
This is why when the various Indian removals of the 1820s and 1830s took place, the land they were sent to ("Indian territory") was initially west of the Mississippi, and later in places like Kansas, the Dakotas and (especially) Oklahoma. These were places that "Americans" had no use for and there were already Indians there, thus proving it would support them. Problems, of course, were that many of the Eastern nations were largely agricultural societies and that there already were Indians living there. Of course, neither was taken much into consideration. Money and farming implements were given (usually far less than promised) and the Indians expected to perform.
As mineral resources (particularly the gold found in the Black Hills—lands sacred to the Sioux Nations) more and more people came into the territory, resulting in violence and helping precipitate the Indian Wars, culminating in incidents like Little Big Horn (1876) and the Massacre at Wounded Knee (1890)—which effectively ended almost all Indian resistance (and hope of regaining their land) on the plains.
The government told the Indians that there was nothing they could do to stem the tide of prospectors and it'd be better to lease or sell the land. After a long legal battle, the Supreme Court ruled in 1980 that the Treaty of Fort Laramie (1851) was valid and the Indians were the rightful owners of the Black Hills (Paha Sapa). They were awarded $105 million. The money sits in a trust fund in their name because accepting it would mean giving up the claim to the land—not to mention it doesn't come even close to comparing to the vast amount of money taken out of the hills, just in gold, let alone other minerals and such (the desire for the return of sacred land is paramount, the rest is merely insulting).
Not coincidentally, the reservations shrunk even further, until the Indians were largely on land that was good for very little. (Even this could be a tenuous hold on the land, as Indians in the Southwest discovered after uranium became a "necessity" of the US.)
Into the "Desert"
Things began to change around mid century as the railroads began to be built across the vast expanses of the plains. This would facilitate travel and railroads would need stop-offs which would facilitate the building of communities. Following the end of the Civil War, the region began seeing more and more inhabitants.
Some of the first people to make use of the plains were cattlemen who found the areas in the southern plains ideal for ranching. They could then drive their herds over the land (grazing as they went) unimpeded to railroad hubs like Abilene, Kansas where the cattle could be sold and shipped back East. Later sheepherders moved in, finding the same assets of the country (the conflict between the two groups erupted into violence in numerous clashes between 1870 and 1900).
While the Homestead Act of 1862 opened up much potential land for settlement, it took some time before the people filtered out onto the plains where they found life difficult and cultivation nearly as bad as it had been claimed decades earlier. But they were also persistent (many were poor and/or recent immigrants who had no place to return to) and full of ingenuity. Crops that were better resistant to the climate were found, irrigation systems built, and better water management skills learned. Still a harsh environment and a hard life, but not "uninhabitable."
More and more people moved into the plains during the 1870s and 1880s. Expansion was helped by better than average rainfall. Of course, droughts began again (as the way to the "dust bowl" conditions was paved)—but what would have probably would have ended most expansion, was only a setback (albeit a serious one) now that the people living on the plains were experienced with the conditions and had ways to combat them.
Still, the plains were not easily domesticated, some parts not being really "settled" until into the twentieth century (western North Dakota and eastern Montana still being thought of as "frontiers" at the turn of the century). What was once merely a barrier to pass through in order to get to the far West was now no longer the great American Desert.
(Sources: www.britannica.com, www.artsci.wustl.edu/~landc/html/pike.html journal entries here, www.kgs.ukans.edu/Publications/primer/primer18.html, www.nebraskastudies.org/0500/stories/0501_0101_02.html Long quotes from here, frontiers.loc.gov/intldl/mtfhtml/mfdev/devagrw.html, Richard Slotkin 1985 The Fatal Environment: the Myth of the Frontier in the Age of Industrialization 1800-1890)