The end of the American Revolution unleased a rush to the frontier of staggering proportions. More so than even the migrations of the 1870s and 80s, Americans in the 1780s and 1790s were on the move. The population of Kentucky, for instance, rose from 12,000 in 1783 to 210,000 by 1800.
As Joyce Appleby notes, Americans in the generation after independence pushed
westward in nearly continuous chains of wagons, seeking new lands. They were
mostly poor farmers, but were confident and aggressive; long before the term
“manifest destiny” was coined, they were making it a reality, and justifying it
with a moral imperative. “Westward migrating families viewed their taking up of
land in the national domain as a movement to spread democratic institutions
across the continent,” Appleby writes. As a traveling British naval officer and
writer, Frederick Marryat would later say of these Americans that “wandering about
seems engrafted in their nature…. They forever imagine that the Lands further
off are still better than those upon which they are already settled.”
|Daniel Boone leading settlers into Kentucky.|
The migrants to the frontier between the Revolution and the War of 1812 were a mix of Southerners and Pennsylvania residents, but they were drawn almost exclusively from the western portions of those states, and the distinction is important. As Frederick Jackson Turner notes in The Significance of the Frontier in American History, before the spread of cotton into the interior of the country, the distinction from Pennsylvania southwards was less North vs. South, but tidewater vs. interior. The mostly poor Westerners chafed at continued political control from the coasts, where many of them had once been indentured servants or had been forced onto marginal land as wealthy landowners had monopolized the best. “The West was not conservative: buoyant, self-confidence and self-assertion were distinguishing traits in its composition,” wrote Turner. The western frontiersman, he added “had little patience with finely drawn distinctions or scruples of method.” He further wrote: “It followed from the lack of organized political life, from the atomic conditions of the backwoods society, that the individual was exalted and given free play. The West was another name for opportunity. Here were mines to be seized; fertile valleys to be pre-empted, all the natural resources open to the shrewdest and the boldest.”
Although Turner’s overall thesis has been successfully challenged on a number of fronts since its appearance, he very correctly stated the frontier belief in opportunity that lay just over the horizon for most settlers. The political allegiance that this opportunity would flower under was, at least in early years, negotiable. As this westward push moved into Kentucky and Tennessee, it was spreading Americans and their traditions, but not inherently spreading American authority. Under the Articles of Confederation, and for some time after the new constitution was adopted, the American identity, like its government, was fragile, contentious, and uncertain. The same forces that unleashed the Whiskey Rebellion in 1791 were pushing migrants further away from their government in space and mind. Some, like Daniel Boone and Moses Austin, crossed into Spanish territory and took that nation’s citizenship. Others flirted with a variety of secessionist movements. Kentucky itself was born as a secession from coastal Virginia. To its restless citizens, who longed for the right to navigate the Mississippi River, if the United States could not provide them with it, they were willing to join any country – or create one if necessary – that could do so. 
There was an alternative to separatism that naturally found more appeal: Western settlers who wanted access to the Mississippi could get it by attacking Spain directly. Spain was a convenient enemy for a number of reasons. Philosophically, Americans saw themselves as inheritors of all European dominions in North America, and for this reason, northern interests coveted Quebec for the same reason that western interests coveted Spanish territory. But Spain in particular was also hated. Americans were Protestant, but Westerners even more so. Americans in large numbers subscribed to a bias known as the “Black Legend” of Spain. “In the popular imagination,” explains Gordon Brown, “Spaniards generally came to be characterized as cruel, tyrannical, superstitious, intolerant or corrupt – or even all of these.” Unlike Canada, moreover, Spain was extremely weak, with an over-extended empire stretching from the borders of Louisiana to Tierra del Fuego, and while its population was large, those provinces closest to America were mostly empty and weakly defended.
|George Rogers Clark|
|The Louisiana Purchase, 1803|
 Laurie Winn Carlson, Seduced by the West: Jefferson’s America and the Lure of the Land Beyond the Mississippi (Chicago: Ivan R. Dee, 2003), 23.
 Joyce Appleby, Inheriting the Revolution: The First Generation of Americans (Cambridge, Mass: Belknap Press, 2001), 53.
 Appleby, 7.
 Frederick Jackson Turner, The Significance of the Frontier in American History (London: Penguin Books, 2008), 28.
 Turner, 21.
 Stagg, 28.
 Brown, 19.
 Brown, 21.
 Carlson, 44.
 Ibid., 52.
 Carlson, 136.
 Brown, 11.