The rest of the continent was not as "wild" and "unknown" as one might think. It was certainly untapped and largely uncharted territory but it was by no means unexplored. The fur trade in particular lead to the dissemination of fur trappers throughout the continent. They knew that the Pacific Ocean lay on the other side of the continent. Anyways back to the question. The Western portion of what is now the continental US was at the time, French, Spanish and British Territories. Spain held territories in Florida and in the southwest in modern California, Texas, etc. Britain held parts of what is now Canada and holdings in the Ohio and Oregon territories which encompassed the Great Lakes and Pacific Northwest regions respectively. Finally the French held territories in Canada as well and in the interior of the continent in what is now known as the Louisiana territory. I'm certain you are familiar with the Louisiana purchase. However I will provide you with a little background to territorial expansion in US at the time and the Louisiana purchase. First the British Ohio territory was ceded to the US by the turn of the century which allowed the US to hold territories in the current states of Ohio, Kentucky, Michigan, Wisconsin, etc. In 1800 Thomas Jefferson became president and he presided over the purchase of Louisiana from the French, who were eager to fund their campaigns in Europe and couldn't hope to defend their American Territories at the same time. This is why when the US approached France with an offer to buy New Orleans, the French offered to sell the entirety of their holdings on the continent to the US. Jefferson eagerly accepted because he had a vision of a largely agrarian, independent yeoman farmer society. In order for the this to happen, the US would need more land however and this would allow the US to double its land mass. This was extremely important for the young nation for industry as well. New Orleans was the connection between the Gulf of Mexico and the Mississippi River which lead all the way up to Missouri River and the Great Lakes basin further north. The Mississippi was the conduit by which the Midwest would grow as they didn't have the same access to the Atlantic that the original colonies inherently had. This was the immediate value of the West, the Annexation of Texas, cession of Mexican land and the Oregon compromise shaped the rest of westward expansion that would occur about four decades later.