The United States' policy during the early to middle nineteenth century can be seen as five general concepts of American foreign policy: isolationism, expansionism, imperialism, idealism, and exceptionalism. Each of these concepts was prevalent during the crisis leading up to and including the Mexican-American War of 1846. The War of 1846 is viewed by Mexico as an act of US imperialism. Brack, a historian, claims that "the process of becoming a continental power required the United States to acquire territory from several nations, but only the acquisition of lands belonging to Mexico required a war...neither France, Spain, nor England ceded to the United States territory contiguous to the homeland as Mexico was requested and then forced to do" (Brown, 54). In other words, the acquisition of Mexican territory through purchase or by conquest was inherent in the basic concept of Manifest Destiny. The precipitating causes of the war are deeply rooted in the domestic and international affairs of the United States and in the personality of President Polk and his insatiable desire to acquire California.
             The desire to acquire territory, especially with ports, fertile soil, and growing markets, led to American interests in the West. Polk saw California as the key to Asian markets and was constantly looking for an excuse to declare war against Mexico and seize its ports. Technological developments brought the country closer together and reduced the detachment of the United States. An increase in immigration led to a growing fear of urbanization, which created a rebirth of Jeffersonian ideology. Domestic malaise also encouraged an adventurous mentality in Americans and a desire to expand. Politically motivated moves by lawmakers in both countries thwarted efforts to come to a bi-lateral agreement. Overall, the Mexican government was considerably weak and simply unable to withstand the military pressure of the United States.
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