The war between the U.S and mexico took place because the U.S decide they wanted to expand across the North American continent, which caused them to clash with all of it's neighbors including the british, the Mexicans and the Native Americans. Americans began migrating to the west even into land that did not belong to the United States.When Plok came into Office in 1845, he believed in the idea of "Manifest Destiny" hwich was the belief that expanding the U.S throughout the continents was both lawful and necessary.
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