Prior to Kansas being admitted into the Union, the Northwest Territory of Kansas was an organized incorporated territory of the United States that existed from May 30, 1854, until January 29, 1861. This land area extended from the Missouri border west to the summit of the Rocky Mountains and from the 37th parallel north to the 40th parallel north. Much of present-day Colorado once was part of the Kansas Territory. The Territory of Colorado was created to govern this western region of the former Kansas Territory on February 28, 1861.
Kansas Territory was established by the Kansas–Nebraska Act, which became a law on May 30, 1854, establishing Nebraska Territory as well as Kansas Territory.
The Act in effect, repealed the Missouri Compromise of 1820, and allowed the settlers of Kansas Territory to determine by popular sovereignty whether Kansas would be a free state or a slave state.
Immediately after the passage of the Kansas–Nebraska Act, hundreds of Missourians crossed into the adjacent territory, rushed for land and gathered together to form solidarity intending to establish a pro-slavery preemption upon the region.
As early as June 10, 1854, a meeting was held at Salt Creek Valley, a trading post located 3 miles west from Fort Leavenworth, at which a “Squatter’s Claim Association” was organized. In unison, they agreed that they were in favor of making Kansas a slave state if it should require half the citizens of Missouri, musket in hand, to emigrate there. According to these emigrants, abolitionists were cautioned not to stop in Kansas Territory, but keep on up the Missouri River until they reach Nebraska Territory, which was anticipated to be a free state. Before the first arrival of Free-State emigrants from the northern and eastern States, nearly every desirable location along the Missouri River had been claimed.
Despite the long debate that preceded the passage of the Kansas-Nebraska Act, it had become the common opinion that the only remaining means whereby the territory might yet be rescued from slave power, was in its immediate occupancy and settlement by anti-slavery emigrants from the free states in sufficient numbers to establish free institutions within its borders. The colonization of the Territory took practical shape while the bill was still under debate in the United States Congress when an organization created for this purpose was the New England Emigrant Aid Company, organized by Eli Thayer.
In 1854, emigration from the free states, which included New England, Iowa, Ohio, and other Midwestern states, flowed into the territory. These emigrants were known as Free-Staters. Because Missourians had claimed much of the land closest to the border, the Free-Staters were forced to establish settlements further into Kansas Territory. Among these inner territories were Lawrence, Topeka, and Manhattan. To protect themselves against the encroachments of non-residents, the “Actual Settlers’ Association of Kansas Territory” was formed.
The last legislative act recorded of the Territorial Legislature was the approval of the charter for the College of the Sisters of Bethany. This was on February 2, 1861, just four days after James Buchanan signed the act of Congress that officially brought Kansas into the Union.