The Western United States, Texas, and the northern territories of the Mexican Empire were an area of ​​expansionist controversy between 1820 and 1860. Antebellum America's expansionism was rooted in a number of current disputes that it turns into a major political issue. Although slavery was one cause of expansion, it was just as important as others; the spread of American institutions, Manifest Destiny, and the protection and prosperity of the nation were equally important. Slavery itself as a cause was rooted in larger causes. The spread of American institutions was a major cause of Western expansion into 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 is clearly reminiscent of the War Hawks' call to invade Canada. This was also the first instance where it was used for American imperialism of which the Mexican-American War is the first act. This was then succeeded by the imperialism of the American takeover of Hawaii and the Spanish-American War. According to President James Polk in his inaugural address (Document F), the American nation and government should expand west to reunite with American settlers through communication, trade, and manufacturing. Charles Summer (Document G) and Reverend William Ellery Channing (Document B) both believed that expansion into Texas was simply an excuse by Southerners to spread the institution of slavery. This works in conjunction with Southern Senator George McDuffie (D... half of document... success and sectoralism of the national economy). Slavery was repeatedly cited 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, including reform movements of which institutions should be spread and which should not, the Southern settlers who wanted to make the manifesto. The destiny that called for slaves to arrive with them and slavery rooted in the nation's current sectionalism and economic prosperity ended up succeeding, but slavery did not happen with the course of the American Civil War. Expansionism in the West eventually led to New Imperialism Since slavery was abolished by the rest of New Imperialism, it can be clearly seen that slavery was not a major cause of Western expansion..