Under such conditions, the maintenance of the senatorial balance of States between the sections would be impossible. Portions of a Northern territory would be applying for admission before population had reached the required number in any Southern part. An additional alarm was felt because every Northern State admitted thus far, having been formed out of the North-west Territory, had incorporated in its constitution the provision of the Ordinance of 1787 that "neither slavery nor involuntary servitude, otherwise than in the punishment of crimes," should ever be permitted. That kept the door of the Northern States closed against the Southern slavery system. Although such action might be held as mandatory on every State created out of the North-west Territory, it could not be so held in States made out of the Louisiana Purchase. Indeed, the treaty of 1803 promised the inhabitants "the free enjoyment of their liberty; property, and religion." So strongly was the Southern element entrenched in national affairs, and so slightly had the ethical views of the Pennsylvania Friends affected the country at large, that the word "property" was tacitly allowed to cover slaves. Louisiana, the first trans-Mississippi State, was admitted with a constitution not prohibiting, and hence permitting slavery. The act changing the Territory of Louisiana, which covered the remainder of the Louisiana Purchase, into the Missouri Territory, passed at the same time, left the Territory open to slavery in the same manner. Slaves could be legally held on the west of the Mississippi as far north as Canada.
This Territory of Missouri, extending from the southern boundary of the State of Arkansas to the Canadian line, received its share of Western migrants. It embraced the heart of the continent. It extended indefinitely up the Missouri River and the Yellowstone, where its traders and trappers came into competition with the outposts of the Hudson Bay and the North-west fur-trading companies, under the protection of a vast system of British troops and outposts. Still farther to the north-west the Americans found the Russian Company, under protection of its Government, taking furs presumably from the Louisiana country to supply Euro-Asia. It is no wonder that American traders began to demand similar protection from their Government. Other industries arising from the rapidly increasing population also demanded attention.