The western United States, Texas, and the northern territories of the Mexican Empire served as an area of ​​expansionist controversy between 1820 and 1860. Expansionism of antebellum America was rooted in a number of current trends. disputes which make it a major political issue. Although slavery was a cause of expansion, it was just as important as any other; Equally important were the spread of American institutions, Manifest Destiny, and the protection and prosperity of the nation. Slavery itself, as a cause, was rooted in more serious causes. The spread of American institutions was a major cause of the western expansion of the United States. According to the editor of the New York Sun (Document H), American expansion will lead to the spread of American ideals of democracy, freedom and republicanism to the West and the "Mexican race." The spread of democracy and American ideals was commonly used as a casus belli, that is, a cause or "excuse" for war, for past and future wars. This clearly recalls the War Hawks' call to invade Canada. This was also the first case of use of this system by American imperialism, of which the Mexican-American War was the first act. This was later followed by imperialism, the capture of Hawaii by the United States and the Spanish-American War. According to President James Polk in his inaugural address (Document F), the American nation and government should expand westward to meet American settlers through communications, commerce, and industry. Charles Summer (Document G) and Rev. William Ellery Channing (Document B) both believed that expansion into Texas was just a pretext for southerners to spread the institution of slavery. This works in conjunction with the national economic success and sectionalism of Southern Senator George McDuffie (D...... middle of paper). Slavery came up repeatedly as a cause of expansion and war, but it was in fact multiple causes, including the spread of American institutions, manifest destiny, and the protection and prosperity of the nation, were deeply rooted in other causes, notably reform movements as to which institutions should be spread and which should not, southern settlers wanting to fulfill the manifesto. The destiny that included the slaves who accompanied them and slavery rooted in the nation's current sectionalism and economic prosperity ultimately succeeded, but slavery did not come to fruition during the American Civil War. Expansionism in the west ultimately resulted in the new imperialism. While slavery was suppressed by the rest of the new imperialism, it is clear that slavery was not a fundamental cause of Western expansion..