Not only did the frontiers expand beyond the seaboard states, but many historians claim that the entire American character changed with the "frontiersmen" and pioneers. "The tremendous shift of population in the early nineteenth century led to the division of old territories and the drawing of new boundaries with bewildering rapidity. Then, as new states were admitted, the political map was stabilized cast of the Mississippi. Within a half-dozen years, six states were created - Indiana in 1816, Mississippi in 1817, Illinois in 1818, Alabama in 1819, Maine in 1820, and Missouri in 1821. The first frontier had been tied closely to Europe, the second to the coast settlements, but the Mississippi Valley was independent and its people looked west rather than east' (Anon 7).
No author listed: "An Outline of American History- From Revolution to Reconstruction"
Both the Articles and the eventual Constitution developed a political group called the "anti-federalists." "The greatest concern of the anti-federalists, in endorsing the Constitution, is that it might diminish the equality of the various states. "The essential feature of the Anti-federalist disposition was not dismemberment of the union; rather the essential 'federal principle' endorsed by a union of equal states" (Allen & Lloyd 2002 77). This the Articles of Confederation also endorsed. The specter of a central government in control seemed to spook many of the Anti-federalists, feeling that the rights of their individual states would now be subservient to a strong central government, where the needs and priorities of the individual states might be secondary.
One of the excuses for continued expansion into lands which were not officially "American" was something called "Manifest Destiny." "The phrase "Manifest Destiny" was first used primarily by Jackson Democrats in the 1840s to promote the annexation of much of what is now the Western United States (