From 1846 to 1848, the United States of America and Mexico went to war. There were several reasons why they did this, three of the most important being Manifest Destiny, the annexation of Texas, and the Slidell Mission. Americans had been gradually moving west for two centuries, but in the 1830s and 1840s they pushed across the continent. Say no to plagiarism. Get a tailor-made essay on "Why Violent Video Games Shouldn't Be Banned"? Get Original EssayAmericans in Texas greatly outnumbered native Mexicans and sought full statehood for the province to gain home rule. Polk appointed John Slidell of Louisiana as minister to Mexico and ordered him to offer up to $30 million to settle disputed claims and purchase California and New Mexico, the territory between Texas and California. Because of Manifest Destiny, the annexation of Texas, and the Slidell mission, the president informed his cabinet that the United States "had ample motive for war." The 1840s were years of extraordinary territorial growth for the United States. During a four-year period, the national domain increased by 1.2 million square miles, an increase of more than sixty percent. The process of territorial expansion was so rapid and dramatic that it came to be seen as an inexorable process, prompting many Americans to insist that their nation had a "manifest destiny" to dominate the continent. The idea of ​​manifest destiny held that Americans were superior to most other peoples in many ways. They were said to have a superior form of government, a superior culture, and a superior religion. For these reasons, it was said, they were destined by God to expand their territory. This attitude led to westward migration. First, it contributed to the expansion of the territory of the United States. It helped lead to the Mexican-American War because it promoted the attitude that America deserved all that land more than the Mexicans. America's God-given destiny made taking land from Mexico acceptable. The same attitude applied to the Indians as American settlers moved west. The idea was that Indians were so inferior that they did not deserve the use of the land. They had to be moved and the land had to go to Americans who deserved it and would use it well. The spirit of “manifest destiny” pervaded the United States during the Reform Era, the decades before the Civil War. John L. O'Sullivan, editor of the influential United States Magazine and Democratic Review, gave his name to the expansionist movement in 1845 when he wrote that it is "the fulfillment of our manifest destiny to extend the continent allotted by Providence for the free development of our millions which multiply every year." Manifest Destiny was spurred by nationalism and an idealistic vision of human perfectibility. It was America's duty to extend freedom and democratic institutions across the continent. Texas gained independence from Mexico in 1836. Initially, the United States refused to incorporate it into the union, largely because Northern political interests were against the addition of a new slave state. Nonetheless, annexation proceedings were quickly initiated following the election of Polk in 1844, who campaigned for the “annexation” of Texas and the “reoccupation of the Oregon Territory.” Polk also had his sights set on California, New Mexico and the rest of what is now the southwestern United States. When his offer to purchase those lands was rejected,.