At this time the Government decided to send out another exploration under Lieutenant John C. Fremont. He entered Kansas in 1842, completing his outfit at the trading post of Cyprian Chouteau in Wyandotte County on June 10. With Kit Carson as a guide, Fremont proceeded to explore the Kansas and Platte Rivers, and to survey the South Pass of the Oregon Trail, thereby winning the title of "Pathfinder." He followed this exploration with three more, in 1843, 1845, and 1848. Accounts of these expeditions were published immediately by the Government to direct attention to the West, and in this they were highly successful.
The war between the United States and Mexico ended with the Treaty of Guadelupe-Hidalgo, ratified May 30, 1848. By its terms, the Rio Grande became the boundary between Texas and Mexico, and the international boundary westward, from El Paso to the Pacific, was established almost as it is now. Northward, the ceded territory reached from a league below San Diego, California, to the Oregon country at 42 north latitude; eastward it reached to the Rocky Mountains. This vast region embraced what was then known as New Mexico and Upper California, and what now corresponds to a strip of Texas;the greater parts of New Mexico, Colorado, and Arizona; all of California, Nevada and Utah; and a little of Wyoming. In addition, the treaty of 1846 with Great Britain had established the right of the United States to the Oregon country. Thus in two years the United States cleared from its continental path to the Pacific all conflicting sovereignties as far north as the forty-ninth parallel.
This resulted in a tremendous increase in migration over Kansas trails. The volume had been swelling since 1843, when the "Great Emigration" to the Oregon country began. Then 900 people in in wagons, and 2,000 horses and cattle, had set out from Elm Grove, Kansas. In 1844 four parties, one of 800 and another of 500 to 700 people, had started westward; and 5,000 had left the Missouri border in 1845. The Mormon trek from Nauvoo, Illinois, "to the western wilderness" started in 1846, and by 1848 most of them had safely reached their new homes in the Salt Lake region. These migrations, however, seem small when compared with that of 1849, when the California gold rush brought 90,000 people through Kansas. Although all these emigrants merely swept through the Kansas country with their eyes fixed on the west, they indirectly affected the region. Civilization was now both west and east of Kansas. In 1850 came the overland stagecoach to Utah and the Pacific coast. The myth of the "Great American Desert" was finally dispelled, and Kansas emerged from obscurity.
The first move to organize Kansas into a Territory, made in 1844, was of small consequence, as were all subsequent movements until 1852. In the spring of that year a half-dozen Missourians met at Union town, Kansas, framed a set of resolutions, which they presented to the Thirty-second Congress, petitioning that the Platte country, comprising the present States of Kansas and Nebraska, be erected into a territory and styled the Nebraska Territory. The bill was not passed.