<P> Adams did much to further this idea . He orchestrated the Treaty of 1818, which established the Canada--US border as far west as the Rocky Mountains, and provided for the joint occupation of the region known in American history as the Oregon Country and in British and Canadian history as the New Caledonia and Columbia Districts . He negotiated the Transcontinental Treaty in 1819, purchasing Florida from Spain and extending the U.S. border with Spanish Mexico all the way to the Pacific Ocean . And he formulated the Monroe Doctrine of 1823, which warned Europe that the Western Hemisphere was no longer open for European colonization . </P> <P> The Monroe Doctrine and manifest destiny formed a closely related nexus of principles: historian Walter McDougall calls manifest destiny a corollary of the Monroe Doctrine, because while the Monroe Doctrine did not specify expansion, expansion was necessary in order to enforce the Doctrine . Concerns in the United States that European powers (especially Great Britain) were seeking to acquire colonies or greater influence in North America led to calls for expansion in order to prevent this . In his influential 1935 study of manifest destiny, Albert Weinberg wrote: "the expansionism of the (1830s) arose as a defensive effort to forestall the encroachment of Europe in North America". </P> <P> Manifest destiny played its most important role in the Oregon boundary dispute between the United States and Britain, when the phrase "manifest desiny" originated . The Anglo - American Convention of 1818 had provided for the joint occupation of the Oregon Country, and thousands of Americans migrated there in the 1840s over the Oregon Trail . The British rejected a proposal by U.S. President John Tyler (in office 1841 - 1845) to divide the region along the 49th parallel, and instead proposed a boundary line farther south along the Columbia River, which would have made most of what later became the state of Washington part of British North America . Advocates of manifest destiny protested and called for the annexation of the entire Oregon Country up to the Alaska line (54 ° 40ʹ N). Presidential candidate James K. Polk used this popular outcry to his advantage, and the Democrats called for the annexation of "All Oregon" in the 1844 U.S. Presidential election . </P> <P> As president, however, Polk sought compromise and renewed the earlier offer to divide the territory in half along the 49th parallel, to the dismay of the most ardent advocates of manifest destiny . When the British refused the offer, American expansionists responded with slogans such as "The Whole of Oregon or None!" and "Fifty - Four Forty or Fight!", referring to the northern border of the region . (The latter slogan is often mistakenly described as having been a part of the 1844 presidential campaign .) When Polk moved to terminate the joint occupation agreement, the British finally agreed in early 1846 to divide the region along the 49th parallel, leaving the lower Columbia basin as part of the United States . The Oregon Treaty of 1846 formally settled the dispute; Polk's administration succeeded in selling the treaty to Congress because the United States was about to begin the Mexican--American War, and the president and others argued it would be foolish to also fight the British Empire . </P>

What period was the peak of manifest destiny